fix libmudflap build failure for 4.1.2 gcc - pass CPP=<target_cpp>, thanks to Hamish Moffatt

toolchain/gcc/gcc-uclibc-3.x.mk

@@ -242,6 +242,7 @@ $(GCC_BUILD_DIR2)/.configured: $(GCC_DIR)/.patched $(GCC_STAGING_PREREQ)
 	(cd $(GCC_BUILD_DIR2); rm -rf config.cache; \
 		$(HOST_CONFIGURE_OPTS) \
 		GCC=$(TARGET_CROSS)gcc \
+		CPP=$(TARGET_CROSS)cpp \
 		LDFLAGS_FOR_TARGET="$(patsubst %,LDFLAGS+=-Wl$(comma)%,$(TARGET_LDFLAGS)) -L$(STAGING_DIR)/lib -L$(STAGING_DIR)/usr/lib" \
 		$(GCC_DIR)/configure \
 		--prefix=$(STAGING_DIR) \
@@ -267,7 +268,7 @@ $(GCC_BUILD_DIR2)/.configured: $(GCC_DIR)/.patched $(GCC_STAGING_PREREQ)
 	touch $@
 
 $(GCC_BUILD_DIR2)/.compiled: $(GCC_BUILD_DIR2)/.configured
-	PATH=$(TARGET_PATH) $(MAKE) $(HOST_CONFIGURE_OPTS) -C $(GCC_BUILD_DIR2) all
+	PATH=$(TARGET_PATH) $(MAKE) $(HOST_CONFIGURE_OPTS) CPP=$(TARGET_CROSS)cpp -C $(GCC_BUILD_DIR2) all
 	touch $@
 
 $(GCC_BUILD_DIR2)/.installed: $(GCC_BUILD_DIR2)/.compiled