Fix -Dwerror=false
    
    Libvirt builds were failing because of:
    
    ../src/util/virconf.c: In function ‘virConfGetValueStringList’:
    ../src/util/virconf.c:950:13: error: Not available before 2.60 [-Werror]
      950 |         G_GNUC_FALLTHROUGH;
          |             ^~~~~~~~~~~~~~~
    cc1: all warnings being treated as errors
    
    -Werror was being passed to GCC.
    
    meson -Dwerror=false was being used which is supposed to disable
    -Werror, but did not do so.
    
    Apparently because of git being used to manage patches, libvirt thinks
    it is being built from git so we need to use:
    
     -Dwerror=false -Dgit_werror=disabled
    
    to really kill off -Werror.