--- a/Makefile.in
+++ b/Makefile.in
@@ -54362,6 +54362,7 @@ configure-target-libphobos:
 	esac; \
 	module_srcdir=libphobos; \
 	rm -f no-such-file || : ; \
+	GDCFLAGS="$(GDCFLAGS_FOR_TARGET)" \
 	CONFIG_SITE=no-such-file $(SHELL) \
 	  $$s/$$module_srcdir/configure \
 	  --srcdir=$${topdir}/$$module_srcdir \
