[RISCV] Add the Sha extension (#113820)

This was introduced in the now-ratified RVA23 profile (and also added to
the RVA22 text) as a simple way of referring to H plus the set of
supervisor extensions required by RVA23.
https://github.com/riscv/riscv-profiles/blob/main/src/rva23-profile.adoc

This patch simply defines the extension. The next patch will adjust the
RVA23 profile to use it, and at that point I think we will be ready to
mark RVA23 as non-experimental.

Note that I haven't made it so if you enable all extensions that
constitute Sha, Sha is implied. Per #76893 (adding 'B'), the concern is
making this implication might break older external assemblers. Perhaps
this is less of a concern given the relative frequency of
`-march=${foo}_zba_zbb_zbs` vs the collection of H extensions. If we did
want to add that implication, we'd probably want to add it in a separate
patch so it can be easily reverted if found to cause problems.

0 files changed, 0 insertions, 0 deletions