Pass CFLAGS_FOR_TARGET/CXXFLAGS_FOR_TARGET to build-gcc-linux.

Makefile.in

@@ -283,7 +283,9 @@ stamps/build-gcc-linux-stage1: $(srcdir)/riscv-gcc stamps/build-binutils-linux \
 		$(GCC_CHECKING_FLAGS) \
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
-		$(WITH_ARCH)
+		$(WITH_ARCH) \
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-gcc
 	$(MAKE) -C $(notdir $@) inhibit-libc=true install-gcc
 	$(MAKE) -C $(notdir $@) inhibit-libc=true all-target-libgcc
@@ -312,7 +314,9 @@ stamps/build-gcc-linux-stage2: $(srcdir)/riscv-gcc $(addprefix stamps/build-glib
 		$(GCC_CHECKING_FLAGS) \
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
-		$(WITH_ARCH)
+		$(WITH_ARCH) \
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	cp -a $(INSTALL_DIR)/$(LINUX_TUPLE)/lib* $(SYSROOT)