[RISCV] Add Xqccmp 0.1 Assembly Support (#128731)
Xqccmp is a new spec by Qualcomm that makes a vendor-specific effort to
solve the push/pop + frame pointers issue. Broadly, it takes the Zcmp
instructions and reverse the order they push/pop registers in, which
ends up matching the frame pointer convention.
This extension adds a new instruction not present in Zcmp,
`qc.cm.pushfp`, which will set `fp` to the incoming `sp` value after it
has pushed the registers.
This change duplicates the Zcmp implementation, with minor changes to
mnemonics (for the `qc.` prefix), predicates, and the addition of
`qc.cm.pushfp`. There is also new logic to prevent combining Xqccmp and
Zcmp. Xqccmp is kept separate to Xqci for decoding/encoding etc, as the
specs are separate today.
Specification:
https://github.com/quic/riscv-unified-db/releases/tag/Xqccmp_extension-0.1.0
