coff-dump.py: Fix PR7996. Now it is compatible to Python-2.4.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@112485 91177308-0d34-0410-b5e6-96231b3b80d8

test/Scripts/coff-dump.py

@@ -397,8 +397,11 @@ def handle_enum(entry):
 		selector = read_value (definitions [0])
 		definitions = definitions [1] [selector]
 
-	description = definitions[value] if value in definitions else "unknown"
-
+	if value in definitions:
+		description = definitions[value]
+	else:
+		description = "unknown"
+
 	write ("%s (" % description)
 	write_value (oformat, value)
 	write (")")