Ensure configuration that defines math_errhandling in <cmath>

...as demanded by the C++17 standard, and required in
sc/source/core/tool/math.cxx.  At least when building an --arch=i386 Flatpak
(where CFLAGS/CXXFLAGS are passed in containing, among others, -O2), that failed
when using -std=gnu++2a (instead of -std=c++2a) due to what looks like an error
in glibc (cf. <https://flathub.org/builds/#/builders/22/builds/797>).

...and fix fallout in external/firebird for Linux x86 32-bit build:  While GCC
defines both __i386 and __i386__ (both as 1) regardless of -std=gnu++* vs.
-std=c++*, it defines i386 (as 1) only for -std=gnu++*.  But various places in
the external/firebird sources check for i386 (among them src/common/common.h,
which fails with

  #error Define FB_CPU for your platform

if i386 is not defined).

Change-Id: I7dce1961c79aeaccc82b1e2bdc350e02730d46af
Reviewed-on: https://gerrit.libreoffice.org/67105
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 7297c72a1db9..bb468640b81e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6241,6 +6241,7 @@ elif test "$GCC" = "yes" -o "$COM_IS_CLANG" = TRUE; then
         ])
         AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
             #include <algorithm>
+            #include <cmath>
             #include <functional>
             #include <vector>
 
@@ -6260,6 +6261,13 @@ elif test "$GCC" = "yes" -o "$COM_IS_CLANG" = TRUE; then
             void f(std::vector<int> & v, std::function<bool(int, int)> fn) {
                 std::sort(v.begin(), v.end(), fn);
             }
+
+            // At least with glibc-headers-2.28-26.fc29.x86_64, when building for Linux x86 32-bit
+            // (via -m32) and passed-in CXXFLAGS setting -O1 (or higher; overriding -Os as set in
+            // solenv/gbuild/platform/LINUX_INTEL_GCC.mk), std=gnu* would cause math_errhandling to
+            // get undef'ed in /usr/include/bits/mathinline.h, while std=c* keeps it defined (as
+            // needed by sc/source/core/tool/math.cxx):
+            int g() { return math_errhandling; }
             ]])],[CXXFLAGS_CXX11=$flag $my_float128hack])
         AC_LANG_POP([C++])
         CXXFLAGS=$save_CXXFLAGS