tools/Makefile: fix HOSTCFLAGS with CROSS_BUILD_TOOLS

When CROSS_BUILD_TOOLS is set, set HOSTCFLAGS to CFLAGS otherwise CC
will be used with HOSTCFLAGS which seems wrong

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
diff --git a/tools/Makefile b/tools/Makefile
index 12a3027..eadeba4 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -272,6 +272,7 @@
 
 ifneq ($(CROSS_BUILD_TOOLS),)
 override HOSTCC = $(CC)
+override HOSTCFLAGS = $(CFLAGS)
 
 quiet_cmd_crosstools_strip = STRIP   $^
       cmd_crosstools_strip = $(STRIP) $^; touch $@