Enable --enable-lto --enable-skia when building with GCC+Clang on Linux

...where all the Library_skia objects are built with Clang, so contain
intermediate LLVM bytecode, but were then linked via GCC and ld or gold, which
do not understand such object files and thus failed.  So in
gb_LinkTarget__command_dynamiclink use T_CC/T_CXX also for the linker command
line.  But then Clang would still be used for linking with the

  -fuse-ld=(ld or gold)

$(USE_LD) suitable for GCC, and would still fail.  So break T_USE_LD out of
T_LDFLAGS and let gb_LinkTarget_use_clang override T_USE_LD with CLANG_USE_LD.
At least for now, that CLANG_USE_LD (containing something like

  -fuse-ld=lld

or

  -fuse-ld=lld --ld-path=...

for the latter see d668c9a04d04d256fcbbd2165fe226f1db88256b "Adapt --enable-ld
to Clang 12 trunk --ld-path") needs to manually be passed into autogen.sh, it is
not computed in configure.ac.

Then building Library_skia would still fail to link against
StaticLibrary_libpng, as that only contains intermediate GCC object code, so
make sure to build it with -ffat-lto-objects in this specific case.

Change-Id: I0a104e53a8898cd9c2eb3b643e21954e853608cc
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/100556
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

11 files changed, 26 insertions, 11 deletions

diff --git a/config_host.mk.in b/config_host.mk.in
index 00288ccb6968..d62afe8e796f 100644
--- a/config_host.mk.in
+++ b/config_host.mk.in
@@ -76,6 +76,7 @@ export CLANG_CXXFLAGS_INTRINSICS_AVX=@CLANG_CXXFLAGS_INTRINSICS_AVX@
 export CLANG_CXXFLAGS_INTRINSICS_AVX2=@CLANG_CXXFLAGS_INTRINSICS_AVX2@
 export CLANG_CXXFLAGS_INTRINSICS_F16C=@CLANG_CXXFLAGS_INTRINSICS_F16C@
 export CLANG_CXXFLAGS_INTRINSICS_FMA=@CLANG_CXXFLAGS_INTRINSICS_FMA@
+export CLANG_USE_LD=@CLANG_USE_LD@
 export CLANGDIR=@CLANGDIR@
 export CLANGLIBDIR=@CLANGLIBDIR@
 export CLANGSYSINCLUDE=@CLANGSYSINCLUDE@
diff --git a/configure.ac b/configure.ac
index dbf13a875ab8..71c395b792e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11500,6 +11500,7 @@ AC_SUBST(CLANG_CXXFLAGS_INTRINSICS_AVX2)
 AC_SUBST(CLANG_CXXFLAGS_INTRINSICS_AVX512)
 AC_SUBST(CLANG_CXXFLAGS_INTRINSICS_F16C)
 AC_SUBST(CLANG_CXXFLAGS_INTRINSICS_FMA)
+AC_SUBST(CLANG_USE_LD)
 
 SYSTEM_GPGMEPP=
 
diff --git a/external/libpng/StaticLibrary_libpng.mk b/external/libpng/StaticLibrary_libpng.mk
index 2d56a276f6a7..8abfdec063db 100644
--- a/external/libpng/StaticLibrary_libpng.mk
+++ b/external/libpng/StaticLibrary_libpng.mk
@@ -44,4 +44,19 @@ $(eval $(call gb_StaticLibrary_add_generated_cobjects,libpng,\
 	) \
 ))
 
+# At least on Linux, with --enable-lto, when building both this external/libpng and external/skia,
+# and building with GCC but building skia with Clang (which should be the sole combination that
+# matches "CLANG_CC is non-empty"), build this as a fat archive (including both the intermediate GCC
+# object code for LTO and machine object code).  Besides targets like Library_vcl (which benefit
+# from the  intermediate GCC object code for LTO), also Library_skia (built with the Clang toolchain
+# lld, which does not understand intermediate GCC object code) includes this, so would otherwise
+# fail to link (but now does not benefit from LTO for this included StaticLibrary_libpng):
+ifeq ($(OS)-$(ENABLE_LTO),LINUX-TRUE)
+ifneq ($(filter SKIA,$(BUILD_TYPE)),)
+ifneq ($(CLANG_CC),)
+$(eval $(call gb_StaticLibrary_add_cflags,libpng,-ffat-lto-objects))
+endif
+endif
+endif
+
 # vim: set noet sw=4 ts=4:
diff --git a/solenv/gbuild/LinkTarget.mk b/solenv/gbuild/LinkTarget.mk
index a18d0a67b1da..98c88a74616b 100644
--- a/solenv/gbuild/LinkTarget.mk
+++ b/solenv/gbuild/LinkTarget.mk
@@ -833,6 +833,7 @@ $(call gb_LinkTarget_get_target,$(1)) : COMPILER_TEST :=
 $(call gb_LinkTarget_get_target,$(1)) : T_SYMBOLS := $(if $(call gb_LinkTarget__symbols_enabled,$(2)),$(true),$(false))
 $(call gb_LinkTarget_get_target,$(1)) : T_CC :=
 $(call gb_LinkTarget_get_target,$(1)) : T_CXX :=
+$(call gb_LinkTarget_get_target,$(1)) : T_USE_LD := $(USE_LD)
 
 ifeq ($(gb_FULLDEPS),$(true))
 ifeq (depcache:,$(filter depcache,$(.FEATURES)):$(gb_PARTIAL_BUILD))
@@ -1784,6 +1785,7 @@ endef
 define gb_LinkTarget_use_clang
 $(call gb_LinkTarget_get_target,$(1)) : T_CC := $(CLANG_CC)
 $(call gb_LinkTarget_get_target,$(1)) : T_CXX := $(CLANG_CXX)
+$(call gb_LinkTarget_get_target,$(1)) : T_USE_LD := $(or $(CLANG_USE_LD),$(USE_LD))
 
 endef
 
diff --git a/solenv/gbuild/platform/android.mk b/solenv/gbuild/platform/android.mk
index 9205e32885e1..d6f4ce42024b 100644
--- a/solenv/gbuild/platform/android.mk
+++ b/solenv/gbuild/platform/android.mk
@@ -32,7 +32,7 @@ $(call gb_Helper_abbreviate_dirs,\
 		-shared \
 		$(if $(filter Library CppunitTest,$(TARGETTYPE)),$(gb_Library_TARGETTYPEFLAGS)) \
 		$(subst \d,$$,$(RPATH)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		$(foreach object,$(COBJECTS),$(call gb_CObject_get_target,$(object))) \
 		$(foreach object,$(CXXOBJECTS),$(call gb_CxxObject_get_target,$(object))) \
 		$(foreach object,$(ASMOBJECTS),$(call gb_AsmObject_get_target,$(object))) \
diff --git a/solenv/gbuild/platform/com_GCC_defs.mk b/solenv/gbuild/platform/com_GCC_defs.mk
index 42d8eefff7fd..0480b0fc3fd5 100644
--- a/solenv/gbuild/platform/com_GCC_defs.mk
+++ b/solenv/gbuild/platform/com_GCC_defs.mk
@@ -37,10 +37,6 @@ endif
 # shell setup (env.vars) for the compiler
 gb_COMPILER_SETUP :=
 
-ifneq ($(USE_LD),)
-gb_LinkTarget_LDFLAGS += $(USE_LD)
-endif
-
 ifeq ($(strip $(gb_COMPILEROPTFLAGS)),)
 gb_COMPILEROPTFLAGS := -O2
 endif
diff --git a/solenv/gbuild/platform/com_MSC_class.mk b/solenv/gbuild/platform/com_MSC_class.mk
index b9bde52cdc01..e184a656f0b4 100644
--- a/solenv/gbuild/platform/com_MSC_class.mk
+++ b/solenv/gbuild/platform/com_MSC_class.mk
@@ -228,7 +228,7 @@ $(call gb_Helper_abbreviate_dirs,\
 			-LIBPATH:$(WINDOWS_SDK_HOME)/lib/x86 \
 			-LIBPATH:$(UCRTSDKDIR)lib/$(UCRTVERSION)/ucrt/x86 \
 			$(if $(filter 80 81 10,$(WINDOWS_SDK_VERSION)),-LIBPATH:$(WINDOWS_SDK_HOME)/lib/$(WINDOWS_SDK_LIB_SUBDIR)/um/x86)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		$(if $(filter Library CppunitTest Executable,$(TARGETTYPE)),/NATVIS:$(SRCDIR)/solenv/vs/LibreOffice.natvis) \
 		@$${RESPONSEFILE} \
 		$(foreach lib,$(sort $(LINKED_LIBS)),$(call gb_Library_get_ilibfilename,$(lib))) \
diff --git a/solenv/gbuild/platform/iOS.mk b/solenv/gbuild/platform/iOS.mk
index dc7d2a8c25d8..6ef7994202e0 100644
--- a/solenv/gbuild/platform/iOS.mk
+++ b/solenv/gbuild/platform/iOS.mk
@@ -88,7 +88,7 @@ define gb_LinkTarget__command_dynamiclink
 	$(if $(CXXOBJECTS)$(OBJCXXOBJECTS)$(GENCXXOBJECTS)$(EXTRAOBJECTLISTS),$(gb_CXX),$(gb_CC)) \
 		$(gb_Executable_TARGETTYPEFLAGS) \
 		$(subst \d,$$,$(RPATH)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		-dead_strip \
 		$(foreach object,$(COBJECTS),$(call gb_CObject_get_target,$(object))) \
 		$(foreach object,$(CXXOBJECTS),$(call gb_CxxObject_get_target,$(object))) \
diff --git a/solenv/gbuild/platform/macosx.mk b/solenv/gbuild/platform/macosx.mk
index c743511207ce..431f8e4b45fc 100644
--- a/solenv/gbuild/platform/macosx.mk
+++ b/solenv/gbuild/platform/macosx.mk
@@ -115,7 +115,7 @@ $(call gb_Helper_abbreviate_dirs,\
 		$(if $(filter Bundle,$(TARGETTYPE)),$(gb_Bundle_TARGETTYPEFLAGS)) \
 		$(if $(filter Library CppunitTest,$(TARGETTYPE)),$(gb_Library_TARGETTYPEFLAGS)) \
 		$(subst \d,$$,$(RPATH)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		$(patsubst lib%.dylib,-l%,$(patsubst %.$(gb_Library_UDK_MAJORVER),%,$(foreach lib,$(LINKED_LIBS),$(call gb_Library_get_filename,$(lib))))) \
 		-Wl$(COMMA)-filelist$(COMMA)$${FILELIST} \
 		$(T_LIBS) \
diff --git a/solenv/gbuild/platform/solaris.mk b/solenv/gbuild/platform/solaris.mk
index d1d068c8fd22..686b082a5cf5 100644
--- a/solenv/gbuild/platform/solaris.mk
+++ b/solenv/gbuild/platform/solaris.mk
@@ -116,7 +116,7 @@ $(call gb_Helper_abbreviate_dirs,\
 		$(if $(SOVERSIONSCRIPT),-Wl$(COMMA)-soname=$(notdir $(1)) \
 			) \
 		$(subst \d,$$,$(RPATH)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		$(foreach object,$(COBJECTS),$(call gb_CObject_get_target,$(object))) \
 		$(foreach object,$(CXXOBJECTS),$(call gb_CxxObject_get_target,$(object))) \
 		$(foreach object,$(ASMOBJECTS),$(call gb_AsmObject_get_target,$(object))) \
diff --git a/solenv/gbuild/platform/unxgcc.mk b/solenv/gbuild/platform/unxgcc.mk
index 6abfb75da4b7..ac6252636fd8 100644
--- a/solenv/gbuild/platform/unxgcc.mk
+++ b/solenv/gbuild/platform/unxgcc.mk
@@ -115,13 +115,13 @@ gb_LinkTarget_CXXFLAGS := $(gb_CXXFLAGS)
 # contains .c sources:
 define gb_LinkTarget__command_dynamiclink
 $(call gb_Helper_abbreviate_dirs,\
-	$(if $(CXXOBJECTS)$(GENCXXOBJECTS)$(EXTRAOBJECTLISTS)$(filter-out XTRUE,X$(ENABLE_RUNTIME_OPTIMIZATIONS)),$(gb_CXX) $(gb_CXX_LINKFLAGS),$(gb_CC)) \
+	$(if $(CXXOBJECTS)$(GENCXXOBJECTS)$(EXTRAOBJECTLISTS)$(filter-out XTRUE,X$(ENABLE_RUNTIME_OPTIMIZATIONS)),$(or $(T_CXX),$(gb_CXX)) $(gb_CXX_LINKFLAGS),$(or $(T_CC),$(gb_CC))) \
 		$(if $(filter Library CppunitTest,$(TARGETTYPE)),$(gb_Library_TARGETTYPEFLAGS)) \
 		$(gb_LTOFLAGS) \
 		$(if $(SOVERSIONSCRIPT),-Wl$(COMMA)--soname=$(notdir $(1)) \
 			-Wl$(COMMA)--version-script=$(SOVERSIONSCRIPT)) \
 		$(subst \d,$$,$(RPATH)) \
-		$(T_LDFLAGS) \
+		$(T_USE_LD) $(T_LDFLAGS) \
 		$(foreach object,$(COBJECTS),$(call gb_CObject_get_target,$(object))) \
 		$(foreach object,$(CXXOBJECTS),$(call gb_CxxObject_get_target,$(object))) \
 		$(foreach object,$(ASMOBJECTS),$(call gb_AsmObject_get_target,$(object))) \