BaseTools: report an error message when failed to start build command

when build.py was failing to build packages but was not providing any
error message except for “Failed to start command.” this patch provide
the error message.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Yonghong Zhu <yonghong.zhu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

BaseTools/Source/Python/build/build.py

@@ -2,7 +2,7 @@
 # build a platform or a module
 #
 #  Copyright (c) 2014, Hewlett-Packard Development Company, L.P.<BR>
-#  Copyright (c) 2007 - 2015, Intel Corporation. All rights reserved.<BR>
+#  Copyright (c) 2007 - 2016, Intel Corporation. All rights reserved.<BR>
 #
 #  This program and the accompanying materials
 #  are licensed and made available under the terms and conditions of the BSD License
@@ -287,6 +287,7 @@ def LaunchCommand(Command, WorkingDir):
         Proc.wait()
     except: # in case of aborting
         # terminate the threads redirecting the program output
+        EdkLogger.quiet("(Python %s on %s) " % (platform.python_version(), sys.platform) + traceback.format_exc())
         if EndOfProcedure != None:
             EndOfProcedure.set()
         if Proc == None: