Don't use orqim on a 16-bit value

Summary: More code that was little-endian specific and getting messed up by the
llvm optimizer. In this case it was combining a write to an ObjectData's
o_attribute and m_count fields, turning the count into garbage and causing the
object to leak. I did some history digging and as far as I can tell, the only
reason this wasn't an orwim to begin with was because it was copied from some
TranslatorX64 code I wrote back in the dark days of the assembler, when we
didn't have a 16-bit version of or.

Reviewed By: @jasone

Differential Revision: D1742340
Fix some repo-mode llvm tests

Summary: - trflags is sometimes nonzero for fallback, so properly implement it
- The comment in ratToAssertType about already knowing Cell and Ref in the jit
   is only true for stack slots, not locals. Losing this type information was
   giving us a Gen base for a minstr instruction, upsetting one of the
   assertions. It was llvm-only because we change the length and shape of
   tracelets by forcing a break after FCall, and this kind of bug tends to
   depend on that.

Reviewed By: @jasone

Differential Revision: D1742487