* configure.ac: Check if C++ compiler supports
-mno-direct-extern-access. Add option to enable building with
-mno-direct-extern-access.
* m4/ax_check_compile_flag.m4: New.
* m4/qt6.m4: Add -mno-direct-extern-access to GPGME_QT6_CFLAGS if
supported and requested.
--
This adds the possibility to build the Qt 6 bindings with the
-mno-direct-extern-access flag. This is required if Qt 6 was built with
this flag. This is a workaround for the lack of Qt 6's pkgconfig files
providing this flag if needed.
GnuPG-bug-id: 6696
