compiletest: //~ ERROR should be interpreted as applying to all revisions

[pnkfelix]

Spawned off of https://github.com/rust-lang/rust/pull/56244/files#r236635792

Right now, you have to write explicit //[rev]~ ERROR annotations for each revision rev in a given test. This is true even when all of the revisions can use identical annotations.

We should change compiletest so that occurrences of //~ ERROR are still parsed and are treated as synonymous for a copy of that same annotation for every revision in the // revisions: set.

[oli-obk]

In some situations it would also have been nice to be able to specify a set of revisions like //[revA revB]~ ERROR.

[tmiasko]

Since #66524 //~ ERROR applies to all revisions, and //[A,B]~ ERROR to revisions A and B.