opts: Fix up -ffold-mem-offsets option keywords

opts: Fix up -ffold-mem-offsets option keywords

While the option was originally meant to be a Target option for a single
target, it is an option for all targets, so should be Common rather than
Target, and because it is an optimization option which could be different
in between different LTO TUs, I've added Optimization keyword too.
From what I can see, Bool is a non-documented non-existing keyword (at
least, grep Bool *.awk shows nothing, so I've dropped that too.  Seems
that the option parsing simply parses and ignores any non-existing keywords.

Guess we should drop the Bool keywords from the gcc/config/riscv/riscv.opt
file eventually, so that people don't copy this around.

2024-01-18  Jakub Jelinek  <jakub@redhat.com>

	PR other/113399
	* common.opt (ffold-mem-offsets): Remove Target and Bool keywords, add
	Common and Optimization.