kbuild: Rename HOSTCXXFLAGS to KBUILD_HOSTCXXFLAGS

In preparation for enabling command line CXXFLAGS, re-name HOSTCXXFLAGS
to KBUILD_HOSTCXXFLAGS as the internal use only flags. This should not
have any visible effects.

Signed-off-by: Laura Abbott <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

Makefile

···
 HOSTCXX      = g++
 KBUILD_HOSTCFLAGS   := -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 \
 		-fomit-frame-pointer -std=gnu89 $(HOST_LFS_CFLAGS)
-HOSTCXXFLAGS := -O2 $(HOST_LFS_CFLAGS)
+KBUILD_HOSTCXXFLAGS := -O2 $(HOST_LFS_CFLAGS)
 HOSTLDFLAGS  := $(HOST_LFS_LDFLAGS)
 HOST_LOADLIBES := $(HOST_LFS_LIBS)
 
···
 export ARCH SRCARCH CONFIG_SHELL HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP HOSTLDFLAGS HOST_LOADLIBES
 export MAKE LEX YACC AWK GENKSYMS INSTALLKERNEL PERL PYTHON PYTHON2 PYTHON3 UTS_MACHINE
-export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
+export HOSTCXX KBUILD_HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
 export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE

scripts/Makefile.host

···
 
 _hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
                  $(HOSTCFLAGS_$(basetarget).o)
-_hostcxx_flags = $(HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
+_hostcxx_flags = $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(basetarget).o)
 
 ifeq ($(KBUILD_SRC),)