diff -rNU3 gcc-9.2.0.old/Makefile.in gcc-9.2.0/Makefile.in
--- gcc-9.2.0.old/Makefile.in	2019-04-09 10:49:14.000000000 +0200
+++ gcc-9.2.0/Makefile.in	2019-11-04 11:45:20.003304394 +0100
@@ -198,6 +198,7 @@
 	AR="$(AR)"; export AR; \
 	AS="$(AS)"; export AS; \
 	CC_FOR_BUILD="$(CC_FOR_BUILD)"; export CC_FOR_BUILD; \
+	CXX_FOR_BUILD="$(CXX_FOR_BUILD)"; export CXX_FOR_BUILD; \
 	DLLTOOL="$(DLLTOOL)"; export DLLTOOL; \
 	LD="$(LD)"; export LD; \
 	LDFLAGS="$(STAGE1_LDFLAGS) $(LDFLAGS)"; export LDFLAGS; \