OE needs to be able to change the default compiler. If we pass in HOSTCC
through the make command, it overwrites not only this setting but also the 
setting in tools/Makefile wrapped in ifneq ($(CROSS_BUILD_TOOLS),) which 
breaks the build.

We therefore add a way of changing the default in the top level Makefile 
without interfering with the other setting.

Upstream-Status: Submitted [emailed to Masahiro Yamada for discussion]
RP 2017/3/11

Index: git/Makefile
===================================================================
--- git.orig/Makefile
+++ git/Makefile
@@ -254,7 +254,8 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH"
 	  else if [ -x /bin/bash ]; then echo /bin/bash; \
 	  else echo sh; fi ; fi)
 
-HOSTCC       = cc
+DEFAULTHOSTCC = cc
+HOSTCC       = $(DEFAULTHOSTCC)
 HOSTCXX      = c++
 HOSTCFLAGS   = -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer \
 		$(if $(CONFIG_TOOLS_DEBUG),-g)