python: Make exception handling Python 3 safe

Change-Id: I9c2cdfad20deb1ddfa224320cf93f2105d126652
Reviewed-on: https://gem5-review.googlesource.com/c/15980
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

src/python/m5/main.py

@@ -209,7 +209,7 @@ def main(*args):
     elif len(args) == 2:
         options, arguments = args
     else:
-        raise TypeError, "main() takes 0 or 2 arguments (%d given)" % len(args)
+        raise TypeError("main() takes 0 or 2 arguments (%d given)" % len(args))
 
     m5.options = options