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 <labbott@redhat.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 09f00da..455d85a 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -64,7 +64,7 @@
 
 _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),)