-mno-direct-extern-access should be added to CFLAGS in pkgconfig files when needed

When Qt is compiled with FEATURE_no_direct_extern_access=ON, the appropriate -mno-direct-extern-access build flags are added to the cmake [1] and qmake [2] build configurations, but not to the pkgconfig files. This causes link failures in projects that use pkgconfig to configure Qt build flags, such as gpgme [3]

[1] https://code.qt.io/cgit/qt/qtbase.git/tree/cmake/QtPlatformTargetHelpers.cmake?h=6.6.0#n48

[2] https://code.qt.io/cgit/qt/qtbase.git/tree/mkspecs/features/unix/no_direct_extern_access.prf?h=6.6.0#n5

[3] https://dev.gnupg.org/T6696