[lit] Fix undefined symbol ArgumentError

Summary:
`ArgumentError` is not defined by the Python standard library.
Executing this line of code would throw a exception, but not the
intended one. It would throw a `NameError` exception, since `ArgumentError`
is undefined.

Use `ValueError` instead, which is defined by the Python standard
library.

Reviewers: echristo, delcypher, beanz, ddunbar

Subscribers: llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D25410

llvm-svn: 283708

llvm/utils/lit/lit/Test.py

@@ -189,9 +189,9 @@ class Test:
 
     def setResult(self, result):
         if self.result is not None:
-            raise ArgumentError("test result already set")
+            raise ValueError("test result already set")
         if not isinstance(result, Result):
-            raise ArgumentError("unexpected result type")
+            raise ValueError("unexpected result type")
 
         self.result = result