Since !5980 (merged) we always enable support for
-rpath. The intention of the change was to enable using
the flag on iOS, tvOS and watchOS by avoiding a Darwin-specific version
check. However, removing the check broke support for OS X 10.4 because
the flag is not supported on that version.
Restore a form of the check that disables the flag on OS X < 10.5 while still allowing it for the other Apple platforms. Since no one is doing iOS/tvOS/etc development on 10.4, this change should have no unintended side effects.
Fixes: #22490 (closed)