Mark the 64-bit x86 push/pop instructions as In64BitMode. Mark the corresponding 32-bit versions with the same encodings Not64BitMode. Remove hack from tablegen disassembler table emitter. Fix bad test.

llvm-svn: 198530

Patch extracted from a larger one by the PaX team. I added the testcases
and tightened error handling a bit.

llvm-svn: 158523