[RFC] Make "run" work on macOS 10.13

[Tom Tromey]

>>>>> "Tom" == Tom Tromey <tom@tromey.com> writes:

Tom> I would like some feedback on this patch.
Tom> On macOS 10.13.5, "run" does not work in gdb.

FWIW this improved gdb.cp/*.exp from 1359 passes to 3296 passes.

Tom