[X86] .code16: temporarily set Mode32Bit when matching an instruction with the data32 prefix
PR47632
This allows MC to match `data32 ...` as one instruction instead of two (data32 without insn + insn).
The compatibility with GNU as improves: `data32 ljmp` will be matched as ljmpl.
`data32 lgdt 4(%eax)` will be matched as `lgdtl` (prefixes: 0x67 0x66, instead
of 0x66 0x67).
GNU as supports many other `data32 *w` as `*l`. We currently just hard code
`data32 callw` and `data32 ljmpw`. Generalizing the suffix replacement is
tricky and requires a think about the "bwlq" appending suffix rules in MatchAndEmitATTInstruction.
Reviewed By: craig.topper
Differential Revision: https://reviews.llvm.org/D88772