Disable guard relaxation for loopy translations

Summary: Also enable fixed-point FrameState for reoptimize(). The legacy
reoptimize is now broken for loopy translations.

Reviewed By: @ottoni, @jdelong

Differential Revision: D1744342

Signature: t1:1744342:1418843317:71dbc7a89cfb0413dcd23723ccfd64e16aeabd9d