We have special logic in `cc` to *not* add RPATH arguments on macOS
when using `-r` as a linker argument, but it's applied every time we
append/extend RPATH lists, and it's not applied consistently.
- [x] Fix this by just not appending *any* parsed RPATHs on macOS
when `-r` is present, instead of handling it on every insertion.
- [x] Simplify logic using the recently added `contains()` function.
Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>
0a385414e5