FILECHECK_OPTS was implemented so that a test runner, such as CI,
can specify FileCheck debugging options, such as -v and -vv.
However, if a test suite has a FileCheck call that already specifies
-v or -vv, then that call will fail if FILECHECK_OPTS also
specifies it.
For -vv, this problem already exists:
clang/test/CodeGen/aarch64-v8.2a-fp16-intrinsics-constrained.c
It's not yet clear if the -vv in that test was intentional, but this
usage shouldn't fail anyway. It's already true that FileCheck permits
-vv and -v together even though -vv implies -v.
Compare D70784, which fixed the same problem for -dump-input.
More than happy for you to make these tidy ups, but can you do them in a separate change, please? It makes it a little trickier to identify which cases existed before, versus which ones are new.