kbuild: Rename HOSTCFLAGS to KBUILD_HOSTCFLAGS

In preparation for enabling command line CFLAGS, re-name HOSTCFLAGS to
KBUILD_HOSTCFLAGS 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 aa971cc..09f00da 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -62,7 +62,7 @@
 #####
 # Handle options to gcc. Support building with separate output directory
 
-_hostc_flags   = $(HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
+_hostc_flags   = $(KBUILD_HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
                  $(HOSTCFLAGS_$(basetarget).o)
 _hostcxx_flags = $(HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
                  $(HOSTCXXFLAGS_$(basetarget).o)