Pass CFLAGS_FOR_TARGET to the newlib libgcc/libc builds

This lets users pass extra CFLAGS to the embedded library builds, which
lets us do things like target the medany code model.

Makefile.in

@@ -226,7 +226,8 @@ stamps/build-gcc-newlib-stage1: $(srcdir)/riscv-gcc stamps/build-binutils-newlib
 		$(GCC_CHECKING_FLAGS) \
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
-		$(WITH_ARCH)
+		$(WITH_ARCH) \
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) all-gcc
 	$(MAKE) -C $(notdir $@) install-gcc
 	mkdir -p $(dir $@) && touch $@
@@ -239,7 +240,8 @@ stamps/build-newlib: $(srcdir)/riscv-newlib stamps/build-gcc-newlib-stage1
 		--prefix=$(INSTALL_DIR) \
 		--enable-newlib-io-long-double \
 		--enable-newlib-io-long-long \
-		--enable-newlib-io-c99-formats
+		--enable-newlib-io-c99-formats \
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
@@ -266,7 +268,8 @@ stamps/build-gcc-newlib-stage2: $(srcdir)/riscv-gcc stamps/build-newlib
 		$(GCC_CHECKING_FLAGS) \
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
-		$(WITH_ARCH)
+		$(WITH_ARCH) \
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@