Issue #9609: Conditionally use G_APPLICATION flag based on GLib version
This attempts to resolve issue #9609 (closed) (for now).
Based on an IRC discussion between @Jehan and @schumaml, it seemed the preferred approach was to follow d16734a4 and use compiler macros for conditional checks. Below GLib 2.74 will use the deprecated G_APPLICATION_FLAGS_NONE
- higher versions of GLib will use G_APPLICATION_DEFAULT_FLAGS
. Eventually this can be removed once the dependency is bumped up.