external/firebird: Work around std::auto_ptr gone from C++17

...which started to be an issue when building with recent Clang 16 trunk after
<https://github.com/llvm/llvm-project/commit/3e99b8d947ac024831e59be2b604ac67a24fed94>
"C++/ObjC++: switch to gnu++17 as the default standard" against libc++:

> src/cloop/Main.cpp:31:12: error: no member named 'auto_ptr' in namespace 'std'
> using std::auto_ptr;
>       ~~~~~^

(Recent versions of GCC similarly default to C++17, but libstdc++ by default
still provides auto_ptr even for C++17.)

Adding -D_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR to CXXFLAGS didn't work, though,
as firebird apparently only honors CXXFLAGS during the configure step, but not
in its makefiles.  So instead add it directly to CXX.  (Adding /all/ the
CXXFLAGS to CXX caused issues at least on Windows, where
<https://ci.libreoffice.org/job/gerrit_windows/135851/> failed with

> Main.cpp
> C:\cygwin\home\tdf\jenkins\workspace\gerrit_windows\workdir\UnpackedTarball\firebird\extern\cloop\src\cloop\Expr.h(25): fatal error C1034: string: no include path set

etc.  This probably needs a general clean-up, and the other *FLAGS passed into
the firebird build system might have a similar issue.)

Change-Id: Idf0a5243938fddfb8348cc960074e60dea775650
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/139932
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

0 files changed, 0 insertions, 0 deletions