[Bug target/109456] `-ffixed` is ignored for `a` registers on RISC-V.

[gccriscvuser at proton dot me via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109456

--- Comment #7 from gccriscvuser at proton dot me ---
To be clear, when I said "generator is emitting correct code", I mean with
respect to the ABI specification.

However, this is an actual bug, not a request for enhancement, because the
emitted code is incorrect with respect to the command-line option.  The
programmer has a reasonable expectation that, if no diagnostic is issued, the
`-ffixed` command-line option is respected.

Thanks