Avoid undefined behaviour in build_option_suggestions

Avoid undefined behaviour in build_option_suggestions

The inner loop in build_option_suggestions uses OPTION to take the
address of OPTB and use it across iterations, which is undefined
behaviour since OPTB is defined within the loop.  Pull it outside the
loop to make this defined.

gcc/ChangeLog:

	* opt-suggestions.cc
	(option_proposer::build_option_suggestions): Pull OPTB
	definition out of the innermost loop.