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>
(cherry picked from commit a9f6e0a4dc)

BaseTools/Source/C/Makefiles/ms.common

@@ -19,8 +19,8 @@
 !ERROR "BASE_TOOLS_PATH is not set! Please run build_tools.bat at first!"
 !ENDIF
 
-!IFNDEF ARCH
-ARCH = IA32
+!IFNDEF HOST_ARCH
+HOST_ARCH = IA32
 !ENDIF
 
 MAKE        = nmake -nologo
@@ -36,7 +36,7 @@ LIB_PATH    = $(BASE_TOOLS_PATH)\Lib
 SYS_BIN_PATH=$(EDK_TOOLS_PATH)\Bin
 SYS_LIB_PATH=$(EDK_TOOLS_PATH)\Lib
 
-!IF "$(ARCH)"=="IA32"
+!IF "$(HOST_ARCH)"=="IA32"
 ARCH_INCLUDE = $(SOURCE_PATH)\Include\Ia32
 BIN_PATH     = $(BASE_TOOLS_PATH)\Bin\Win32
 LIB_PATH     = $(BASE_TOOLS_PATH)\Lib\Win32
@@ -44,7 +44,7 @@ SYS_BIN_PATH = $(EDK_TOOLS_PATH)\Bin\Win32
 SYS_LIB_PATH = $(EDK_TOOLS_PATH)\Lib\Win32
 !ENDIF
 
-!IF "$(ARCH)"=="X64"
+!IF "$(HOST_ARCH)"=="X64"
 ARCH_INCLUDE = $(SOURCE_PATH)\Include\X64
 BIN_PATH     = $(BASE_TOOLS_PATH)\Bin\Win64
 LIB_PATH     = $(BASE_TOOLS_PATH)\Lib\Win64