Turn on my codegen prepare heuristic by default. It doesn't affect

Turn on my codegen prepare heuristic by default.  It doesn't affect
performance in most cases on the Grawp tester, but does speed some
things up (like shootout/hash by 15%).  This also doesn't impact
compile time in a noticable way on the Grawp tester.

It also, of course, gets the testcase it was designed for right :)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60120 91177308-0d34-0410-b5e6-96231b3b80d8