bug#24884: Segfault on (mkstemp! "XX" 0)

[Matt Wette]

Please check 24862, which includes a patch: 
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=24862 
<https://debbugs.gnu.org/cgi/bugreport.cgi?bug=24862>

The issue is that (at least on Mac OS 10.12) mkstemp will only accept specific 
flags.