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/gcc/mingw-gcc-build.py

@@ -337,7 +337,7 @@ class SourceFiles:
                     print '[KeyboardInterrupt]'
                     return False
 
-                except Exception, e:
+                except Exception as e:
                     print e
 
             if not completed: return False