BaseTools: Refactor python except statements

Convert "except ... ," to "except ... as" to be compatible with python3.
Based on "futurize -f lib2to3.fixes.fix_except"

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

BaseTools/Source/Python/AutoGen/GenMake.py

@@ -1030,7 +1030,7 @@ cleanlib:
             else:
                 try:
                     Fd = open(F.Path, 'r')
-                except BaseException, X:
+                except BaseException as X:
                     EdkLogger.error("build", FILE_OPEN_FAILURE, ExtraData=F.Path + "\n\t" + str(X))
 
                 FileContent = Fd.read()