revert CXX_FOR_BUILD stuff, breaks gcj compile

mk/build.mk

@@ -266,7 +266,7 @@ ifeq ($(filter-out distclean,${MAKECMDGOALS}),)
 include ${TOPDIR}/mk/vars.mk
 else
 include $(TOPDIR)/prereq.mk
-export BASH MAKE LANGUAGE LC_ALL OStype PATH CC_FOR_BUILD CXX_FOR_BUILD QEMU
+export BASH MAKE LANGUAGE LC_ALL OStype PATH CC_FOR_BUILD QEMU
 endif
 
 all: menuconfig

mk/vars.mk

@@ -140,7 +140,6 @@ TARGET_CONFIGURE_OPTS=	PATH='${TARGET_PATH}' \
 			CROSS='$(TARGET_CROSS)'
 
 HOST_CONFIGURE_OPTS=	CC_FOR_BUILD='${CC_FOR_BUILD}' \
-			CXX_FOR_BUILD='${CXX_FOR_BUILD}' \
 			CPPFLAGS_FOR_BUILD='${CPPFLAGS_FOR_BUILD}' \
 			CFLAGS_FOR_BUILD='${CFLAGS_FOR_BUILD}' \
 			LDFLAGS_FOR_BUILD='${LDFLAGS_FOR_BUILD}' \