[committed] Fix rv32 issues with recent zicboz work

[committed] Fix rv32 issues with recent zicboz work

I should have double-checked the CI system before pushing Christoph's patches
for memset-zero.  While I thought I'd checked CI state, I must have been
looking at the wrong patch from Christoph.

Anyway, this fixes the rv32 ICEs and disables one of the tests for rv32.

The test would need a revamp for rv32 as the expected output is all rv64 code
using "sd" instructions.  I'm just not vested deeply enough into rv32 to adjust
the test to work in that environment though it should be fairly trivial to copy
the test and provide new expected output if someone cares enough.

Verified this fixes the rv32 failures in my tester:
> New tests that FAIL (6 tests):
>
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O1  (internal compiler error: in extract_insn, at recog.cc:2812)
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O1  (test for excess errors)
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O2  (internal compiler error: in extract_insn, at recog.cc:2812)
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O2  (test for excess errors)
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O3 -g  (internal compiler error: in extract_insn, at recog.cc:2812)
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O3 -g  (test for excess errors)

And after the ICE is fixed, these are eliminated by only running the test for
rv64:

> New tests that FAIL (3 tests):
>
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O1   check-function-bodies clear_buf_123
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O2   check-function-bodies clear_buf_123
> unix/-march=rv32gcv: gcc: gcc.target/riscv/cmo-zicboz-zic64-1.c   -O3 -g   check-function-bodies clear_buf_123

gcc/
	* config/riscv/riscv-string.cc
	(riscv_expand_block_clear_zicboz_zic64b): Handle rv32 correctly.

gcc/testsuite

	* gcc.target/riscv/cmo-zicboz-zic64-1.c: Don't run on rv32.