Repair macOS build

Avoid macro redefinition of `open' in lib/fcntl.h to break use of it as
a struct member in src/font.c.

* src/font.c: #undef open
1 job for master in 52 minutes and 30 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #2445
test-all

00:52:30

 
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