BaseTools: Replace ARCH with HOST_ARCH in C Makefile to avoid conflict

BaseTools: Replace ARCH with HOST_ARCH in C Makefile to avoid conflict

https://bugzilla.tianocore.org/show_bug.cgi?id=793

ARCH is too generic. It may cause confuse of target arch or host arch.
To be clarified, replace it with HOST_ARCH in BaseTools C Makefile.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Yonghong Zhu <yonghong.zhu@intel.com>