RISC-V: Document optimization parameter riscv-strcmp-inline-limit

RISC-V: Document optimization parameter riscv-strcmp-inline-limit

This patch documents the optimization parameter
riscv-strcmp-inline-limit, which can be used to tweak the behaviour
of -minline-strcmp and -minline-strncmp.

gcc/ChangeLog:

	PR target/112650
	* doc/invoke.texi: Document riscv-strcmp-inline-limit.

Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>