Update mini-gmp

* src/mini-gmp.c: Sync from upstream.  This incorporates:
2019-08-13 Silence a couple of warnings
1 job for master in 58 minutes and 36 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #3051
test-all

00:58:36

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:959: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1