Pass @cmodel@ to CXXFLAGS (is similar to CFLAGS).

Makefile.in

@@ -55,6 +55,7 @@ LINUX_TUPLE  ?= $(call make_tuple,$(XLEN),linux-gnu)
 NEWLIB_TUPLE ?= $(call make_tuple,$(XLEN),elf)
 
 CFLAGS_FOR_TARGET := $(CFLAGS_FOR_TARGET_EXTRA) @cmodel@
+CXXFLAGS_FOR_TARGET := $(CXXFLAGS_FOR_TARGET_EXTRA) @cmodel@
 ASFLAGS_FOR_TARGET := $(ASFLAGS_FOR_TARGET_EXTRA) @cmodel@
 # --with-expat is required to enable XML support used by OpenOCD.
 BINUTILS_TARGET_FLAGS := --with-expat=yes $(BINUTILS_TARGET_FLAGS_EXTRA)
@@ -237,6 +238,7 @@ endif
 	cd $(notdir $@) && \
 		CC="$(GLIBC_CC_FOR_TARGET) $($@_CFLAGS)" \
 		CFLAGS="$(CFLAGS_FOR_TARGET) -g -O2 $($@_CFLAGS)" \
+		CXXFLAGS="$(CXXFLAGS_FOR_TARGET) -g -O2 $($@_CFLAGS)" \
 		ASFLAGS="$(ASFLAGS_FOR_TARGET) $($@_CFLAGS)" \
 		$</configure \
 		--host=$(call make_tuple,$($@_XLEN),linux-gnu) \
@@ -430,7 +432,8 @@ stamps/build-gcc-newlib-stage1: $(srcdir)/riscv-gcc stamps/build-binutils-newlib
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
 		$(WITH_ARCH) \
-		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@) all-gcc
 	$(MAKE) -C $(notdir $@) install-gcc
 	mkdir -p $(dir $@) && touch $@
@@ -445,7 +448,8 @@ stamps/build-newlib: $(srcdir)/riscv-newlib stamps/build-gcc-newlib-stage1
 		--enable-newlib-io-long-double \
 		--enable-newlib-io-long-long \
 		--enable-newlib-io-c99-formats \
-		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
@@ -469,7 +473,8 @@ stamps/build-newlib-nano: $(srcdir)/riscv-newlib stamps/build-gcc-newlib-stage1
 		--disable-newlib-supplied-syscalls \
 		--disable-nls \
 		--enable-newlib-register-fini \
-		CFLAGS_FOR_TARGET="-Os -ffunction-sections -fdata-sections $(CFLAGS_FOR_TARGET)"
+		CFLAGS_FOR_TARGET="-Os -ffunction-sections -fdata-sections $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os -ffunction-sections -fdata-sections $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@
@@ -519,7 +524,8 @@ stamps/build-gcc-newlib-stage2: $(srcdir)/riscv-gcc stamps/build-newlib \
 		$(MULTILIB_FLAGS) \
 		$(WITH_ABI) \
 		$(WITH_ARCH) \
-		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)"
+		CFLAGS_FOR_TARGET="-Os $(CFLAGS_FOR_TARGET)" \
+		CXXFLAGS_FOR_TARGET="-Os $(CXXFLAGS_FOR_TARGET)"
 	$(MAKE) -C $(notdir $@)
 	$(MAKE) -C $(notdir $@) install
 	mkdir -p $(dir $@) && touch $@