test/coff-dump: Support reading from stdin.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115640 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Scripts/coff-dump.py b/test/Scripts/coff-dump.py
index 7868c00..d734f0a 100755
--- a/test/Scripts/coff-dump.py
+++ b/test/Scripts/coff-dump.py
@@ -560,7 +560,12 @@
 
   return handlers[entry[0]](entry)
 
-Input = open (sys.argv[1], "rb")
+if len(sys.argv) <= 1 or sys.argv[1] == '-':
+  import StringIO
+  Input = StringIO.StringIO(sys.stdin.read())
+else:
+  Input = open (sys.argv[1], "rb")
+
 try:
   handle_element(file)
 finally: