[RISC-V][PR target/119830] Fix RISC-V codegen on 32bit hosts

[RISC-V][PR target/119830] Fix RISC-V codegen on 32bit hosts

So this is Andrew's patch from the PR.  We weren't clean for a 32bit host in
some of the arithmetic for constant synthesis.

I confirmed the bug on a 32bit linux host, then confirmed that Andrew's patch
from the PR fixes the problem, then ran Andrew's patch through my tester
successfully.

Naturally I'll wait for pre-commit testing, but I'm not expecting problems.

	PR target/119830
gcc/
	* config/riscv/riscv.cc (riscv_build_integer_1): Make arithmetic in bclr case
	clean for 32 bit hosts.

gcc/testsuite/
	* gcc.target/riscv/pr119830.c: New test.