PKG_KEEP_SYSTEM_CFLAGS
{ "keep-system-cflags", no_argument, &want_flags, PKG_KEEP_SYSTEM_CFLAGS, },
if (!(want_flags & PKG_KEEP_SYSTEM_CFLAGS) && pkgconf_fragment_has_system_dir(client, frag))
want_flags |= PKG_KEEP_SYSTEM_CFLAGS;