[Bug target/112397] Two persistent libstdc++ test failures on x86_64-apple-darwin

["iains at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112397

--- Comment #10 from Iain Sandoe <iains at gcc dot gnu.org> ---
automake if is limited to testing a single variable, so we have to introduce an
AM_CONDITIONAL to say the OS is DARWIN (we did not seem to have one already,
but I could have missed something else usable).

I'm testing this - if it's not too invasive (but I'll also try, at some point,
to see if applying this to the whole library build makes any measurable
performance change)

diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index c68cac4f345..37396bd6ebb 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -109,6 +109,12 @@ ACX_LT_HOST_FLAGS
 AC_SUBST(enable_shared)
 AC_SUBST(enable_static)
 AM_CONDITIONAL([ENABLE_DARWIN_AT_RPATH], [test x$enable_darwin_at_rpath =
xyes])
+os_is_darwin=no
+case ${host_os} in
+  darwin*) os_is_darwin=yes ;;
+  *) ;;
+esac
+AM_CONDITIONAL([OS_IS_DARWIN], [test x${os_is_darwin} = xyes])

 if test "$enable_vtable_verify" = yes; then
   predep_objects_CXX="${predep_objects_CXX}
${glibcxx_builddir}/../libgcc/vtv_start.o"
diff --git a/libstdc++-v3/libsupc++/Makefile.am
b/libstdc++-v3/libsupc++/Makefile.am
index d0e1618507e..645d53cb6ab 100644
--- a/libstdc++-v3/libsupc++/Makefile.am
+++ b/libstdc++-v3/libsupc++/Makefile.am
@@ -132,6 +132,14 @@ atomicity_file =
${glibcxx_srcdir}/$(ATOMICITY_SRCDIR)/atomicity.h
 atomicity.cc: ${atomicity_file}
        $(LN_S) ${atomicity_file} ./atomicity.cc || true

+if OS_IS_DARWIN
+# See PR 112397
+new_opvnt.lo: new_opvnt.cc
+       $(LTCXXCOMPILE) -fno-reorder-blocks-and-partition -I. -c $<
+new_opvnt.o: new_opvnt.cc
+       $(CXXCOMPILE) -fno-reorder-blocks-and-partition -I. -c $<
+endif
+
 # AM_CXXFLAGS needs to be in each subdirectory so that it can be
 # modified in a per-library or per-sub-library way.  Need to manually
 # set this option because CONFIG_CXXFLAGS has to be after