This commit adds new compiler options -no-warning-as-error/-warning-as-error which allows users to specify behavior for exact warnings and warning groups.
Although I don't plan to bring over new assertions wholesale
into the current qualification branch, it's entirely possible
that various minor changes in main will use the new assertions;
having this basic support in the release branch will simplify that.
(This is why I'm adding the includes as a separate pass from
rewriting the individual assertions)
Moving generic constraint from extension to its member or vice versa may change the mangled name
of the member without changing the generic signature, thus introducing ABI breakages. This change
teaches the ABI checker to diagnose USR (mangled name) changes to cover such cases.
rdar://78276290
