[PATCH] RISC-V: Support riscv bitmanip frozen ZBA/ZBB/ZBC instructions (v0.93).

[Jim Wilson]

You dropped the -menable-experimental-extensions option.  You are allowing
zba/zbb/zbc support without explicit versions.  And you are mapping B to
zba/zbb/zbc.  Are you sure we want to do that?  Just because it is "frozen"
doesn't mean that it won't change again.  It just means it is less likely
to change again.

I'm also concerned about the number of changes being made to the B spec
right before the Binutils release branch is made.  Some of these changes
just came through on Monday this week.  That isn't enough time for
simulator support and cross checking the assembler against the simulator to
verify it.  So do we really want to ship an assembler with an untested
unverified B extension implementation?  Without the
-menable-experimental-extensions option?  This could come back and bite us
in the future if we find bugs, or people design hardware using this
"frozen" implementation and the final one turns out to be different.

Jim