Fix some llvm issues from test/slow

Summary: - Fix a few places in code-gen-x64.cpp that should've been defining i8, not i64
- Split asInt into zext and narrow, requiring callers to be more explicit
- Class::classof can return a bool now that we handle it properly in the jit
- Add --llvm option to test/run
- Move some tracing around to make debugging locrec issues easier

Reviewed By: @jasone

Differential Revision: D1738588

Signature: t1:1738588:1418673994:fa8a102ab6bed3102f7fc2c9c0b7abb3ec4a276d
Fix ReflectionParameter::getClass() for self

Summary: fixes facebook/hhvm#4465

{sync, type="child", parent="internal", parentrevid="1742311", parentrevfbid="731149410302611", parentdiffid="5962255"}

Reviewed By: @JoelMarcey

Differential Revision: D1742311

Signature: t1:1742311:1418744128:2a04ebe20d1d47c81d9c4a01c949badbe4487389