[committed] declare variant scoring when at least one variant needs to be deferred

Hi! The following patch is in preparation of the deferred declare variant resolution, where we need to compute the scores during gimplification for all variants. This patch just picks the candidate with highest score if that variant doesn't need to be deferred and thus is an unconditional win, but

[committed] declare variant scoring

Hi! The following patch implements the scoring, except it doesn't handle the case when a call is nested in 188+ OpenMP constructs yet. At least in the current standard wording, the score can be a sum of up to 8 2^X numbers where X is quite arbitrary constant (because the construct nesting depth c