RISC-V: Add vectorized strlen.

RISC-V: Add vectorized strlen.

This patch implements a vectorized strlen by re-using and slightly
adjusting the rawmemchr implementation.  Rawmemchr returns the address
of the needle while strlen returns the difference between needle address
and start address.

As before, strlen expansion is guarded by -minline-strlen.

While testing with -minline-strlen I encountered a vsetvl problem in
memcpy-chk.c where we didn't insert a vsetvl at the proper spot (after
a setjmp).  This needs to be fixed separately and I figured I'd post
this patch as-is.

gcc/ChangeLog:

	PR target/112109

	* config/riscv/riscv-protos.h (expand_rawmemchr): Add strlen
	parameter.
	* config/riscv/riscv-string.cc (riscv_expand_strlen): Call
	rawmemchr.
	(expand_rawmemchr): Add strlen handling.
	* config/riscv/riscv.md: Add TARGET_VECTOR to strlen expander.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/builtin/strlen-run.c: New test.
	* gcc.target/riscv/rvv/autovec/builtin/strlen.c: New test.