Move RUN line to top of file

Author: David Ungar

test/NameBinding/custom-attr-on-extension.swift

@@ -1,8 +1,9 @@
+// RUN: %target-swift-frontend -typecheck %s -verify
+
 // Trips an assertion if an ASTScope lookup is attempted into the innermost
 // DeclContext of the extension.
 
 struct Ty{}
 
 @foo extension Ty {} // expected-error {{unknown attribute 'foo'}}
 
-// RUN: %target-swift-frontend -typecheck %s -verify