external/libodfgen: Honor -std=... passed in via CXXFLAGS

...which fixes an issue encountered when compiling with Clang against trunk
libstdc++ (which contains pre-C++17-only code that triggers
<https://bugs.llvm.org/show_bug.cgi?id=41896> "Bogus 'error: no return statement
in constexpr function' when void return type is 'templated'")

Change-Id: I33368996c8ac8cf32893ba1b631ace2a606dafb1
Reviewed-on: https://gerrit.libreoffice.org/72409
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

external/libodfgen/UnpackedTarball_libodfgen.mk

@@ -35,8 +35,12 @@ $(eval $(call gb_UnpackedTarball_add_patches,libodfgen, \
 endif
 endif
 
+# * external/libodfgen/c++11.patch: obsoleted upstream by
+#   <https://sourceforge.net/p/libwpd/libodfgen/ci/e11112e50562de4f3252227bfba175ededf82194/>
+#   "boost::shared_ptr -> std::shared_ptr"
 $(eval $(call gb_UnpackedTarball_add_patches,libodfgen, \
 	external/libodfgen/0001-tdf-101077-make-double-string-conversion-locale-agno.patch.1 \
+	external/libodfgen/c++11.patch \
 ))
 
 # vim: set noet sw=4 ts=4:

external/libodfgen/c++11.patch

+# Add -std=c++11 before existing CXXFLAGS, in case those already contain some -std= (which will thus
+# override the preceding -std=c++11, which is likely what the caller passing in those CXXFLAGS
+# intends):
+#
+#--- configure.ac
+#+++ configure.ac
+#@@ -217,7 +217,7 @@
+# AS_IF([test "x$with_sharedptr" = "xc++11"], [
+#     AC_MSG_CHECKING([for c++11 shared ptr])
+#     save_CXXFLAGS="$CXXFLAGS"
+#-    CXXFLAGS="$CXXFLAGS -std=c++11"
+#+    CXXFLAGS="-std=c++11 $CXXFLAGS"
+#     AC_COMPILE_IFELSE([
+#         AC_LANG_PROGRAM(
+#             [[#include <memory>]],
+#@@ -241,7 +241,7 @@
+#         AC_MSG_RESULT([no])
+#     ], [
+#         AC_MSG_RESULT([yes])
+#-        CXXFLAGS="$CXXFLAGS -std=c++11"
+#+        CXXFLAGS="-std=c++11 $CXXFLAGS"
+#     ])
+# ])
+# AS_IF([test "x$with_sharedptr" = "xtr1"], [
+--- configure
++++ configure
+@@ -16723,7 +16723,7 @@
+     { $as_echo "$as_me:${as_lineno-$LINENO}: checking for c++11 shared ptr" >&5
+ $as_echo_n "checking for c++11 shared ptr... " >&6; }
+     save_CXXFLAGS="$CXXFLAGS"
+-    CXXFLAGS="$CXXFLAGS -std=c++11"
++    CXXFLAGS="-std=c++11 $CXXFLAGS"
+     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+ /* end confdefs.h.  */
+ 
+@@ -16780,7 +16780,7 @@
+ 
+         { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
+ $as_echo "yes" >&6; }
+-        CXXFLAGS="$CXXFLAGS -std=c++11"
++        CXXFLAGS="-std=c++11 $CXXFLAGS"
+ 
+ fi
+ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext