llvm-mc/AsmParser: Separate instruction ordering for ambiguity detection.

 - We want the ordering operation to be simple, since we run it on every
   match. The old ordering is also not a strict weak ordering when there are
   ambiguities, which makes MSVC unhappy.

 - While we are at it, detect all ambiguities instead of just the adjacent
   ones. There are actually 655, for X86.

llvm-svn: 78526