Always execute tests internally on Windows.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@82542 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/lit.cfg b/test/lit.cfg
index 450b614..2f6e945 100644
--- a/test/lit.cfg
+++ b/test/lit.cfg
@@ -1,6 +1,7 @@
 # -*- Python -*-
 
 import os
+import platform
 
 # Configuration file for the 'lit' test runner.
 
@@ -11,7 +12,8 @@
 #
 # For now we require '&&' between commands, until they get globally killed and
 # the test runner updated.
-config.test_format = lit.formats.ShTest(execute_external = True,
+execute_external = platform.system() != 'Windows'
+config.test_format = lit.formats.ShTest(execute_external,
                                         require_and_and = True)
 
 # suffixes: A list of file extensions to treat as test files.