Require intervals in the range metadata to be in a canonical form: They must

Require intervals in the range metadata to be in a canonical form: They must
be non contiguous, non overlapping and sorted by the lower end.

While this is technically a backward incompatibility, every frontent currently
produces range metadata with a single interval and we don't have any pass
that merges intervals yet, so no existing bitcode files should be rejected by
this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157741 91177308-0d34-0410-b5e6-96231b3b80d8