Disable message box when calling abort(). The message box is causing hangs in tests.

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>
6 jobs for gitlab-cmake in 4 minutes and 56 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #10290
docker
autoconf

00:04:56

passed #10291
docker
cmake

00:02:02

 
  External
failed continuous-integration/appveyor/branch

failed continuous-integration/appveyor/merge-request

passed continuous-integration/appveyor/branch

canceled continuous-integration/appveyor/branch