--- gcc-4.8.1/Makefile.in.orig
+++ gcc-4.8.1/Makefile.in
@@ -169,6 +169,7 @@
 # built for the build system to override those in BASE_FLAGS_TO_PASSS.
 EXTRA_BUILD_FLAGS = \
 	CFLAGS="$(CFLAGS_FOR_BUILD)" \
+	CXXFLAGS="$(CXXFLAGS_FOR_BUILD)" \
 	LDFLAGS="$(LDFLAGS_FOR_BUILD)"
 
 # This is the list of directories to built for the host system.
