Try to fix compiler-rt tests after 87dbdd2e on mac and win

These tests use `--check-prefix=CHECK-%os` but then didn't have
a CHECK line for every os.

In most tests, the linux expectations were sufficient (they match
the "wrap_" prefix with .*), so just remove the check-prefix there.
In the places where this didn't easily work, make sure there are
at least CHECK-Windows and CHECK-Darwin lines.