[nfc] Add _builtin suffix to moveonly builtin tests.

This will make it clearer what these tests are actually not meant to check the
move checker and are instead just meant to test our emission of the builtin.

Author: gottesmm

test/SILGen/moveonly.swift renamed to test/SILGen/moveonly_builtin.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-emit-silgen -parse-stdlib %s -disable-access-control -disable-objc-attr-requires-foundation-module | %FileCheck %s
+// RUN: %target-swift-emit-silgen -module-name moveonly -parse-stdlib %s -disable-access-control -disable-objc-attr-requires-foundation-module | %FileCheck %s
 
 import Swift