groups/010.host_deps.group:flex_host:${PKG_CFLAGS_CONFIGURE_EXTRA}: configure w/ -D_GNU_SOURCE.
groups/221.native_packages_dev.group:flex:${PKG_CFLAGS_CONFIGURE_EXTRA}: configure w/ -D_GNU_SOURCE.
groups/dev_packages.group:flex:${PKG_CFLAGS_CONFIGURE_EXTRA}: configure w/ -D_GNU_SOURCE.