[Bug target/106530] New: RISCV documentation for -march= is very lacking

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106530

            Bug ID: 106530
           Summary: RISCV documentation for -march= is very lacking
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: documentation
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---
            Target: riscv*-*-*

The current documentation for -march= does not specify what extensions are
valid or really anything.
It just shows examples.

The documentation should say what each letter corresponds to and maybe even
point to the specifications link.

E.g. what does 'rv32iabmc' mean?