unify HOST_CFLAGS and HOSTCFLAGS

The top build system sets up HOSTCFLAGS a bit and exports it, but other
places use HOST_CFLAGS instead.  Unify the two as HOSTCFLAGS so that the
values stay in sync.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/Makefile b/Makefile
index a7ffe25..ebdf032 100644
--- a/Makefile
+++ b/Makefile
@@ -429,7 +429,7 @@
 	@$(XECHO) Generating $@ ; \
 	set -e ; \
 	: Generate the dependancies ; \
-	$(CC) -x c -DDO_DEPS_ONLY -M $(HOST_CFLAGS) $(CPPFLAGS) \
+	$(CC) -x c -DDO_DEPS_ONLY -M $(HOSTCFLAGS) $(CPPFLAGS) \
 		-MQ $(obj)include/autoconf.mk include/common.h > $@
 
 $(obj)include/autoconf.mk: $(obj)include/config.h