createProcess ENOENT regression on mac OS

[elaforge]

This may be the same issue as #224, but it's on mac OS so I thought I'd mention it separately. I tried to test out the fix at #232, but I got a segfault and couldn't figure out if it's because I compiled it wrong or if it's actually broken. Anyway, for completeness:

ghc 8.8.3, process-1.6.8.0:

Prelude> import System.Process
Prelude System.Process> createProcess (proc "aoeu" [])
*** Exception: aoeu: createProcess: runInteractiveProcess: exec: does not exist
(No such file or directory)

ghc 9.2.1, process-1.6.13.2:

Prelude> import System.Process
Prelude System.Process> createProcess (proc "aoeu" [])
*** Exception: aoeu: createProcess: posix_spawnp: failed (Undefined error: 0)

ghc 8.8.3, process 1.6.14.0, via cabal v1-repl:

*System.Cmd> import System.Process
*System.Cmd System.Process> createProcess (proc "aoeu" [])
[1]    98747 segmentation fault  cabal v1-repl

I also noticed that ./configure mentioned this:

checking whether posix_spawn reports errors sensibly... yes

This makes me think either darwin is non-sensible in some other way, or this is not #224 after all.

[snoyberg]

Pinging @bgamari