build: Mismatch between gint64 and int64_t in OSX 64-bit
Check for compile warnings when assigning an int64_t* to a long*, make gint64 a long long if they occur and assigning an int64_t* to a long long* doesn't.
Modified by Philip Withnall firstname.lastname@example.org to support Meson as well as autotools.
Closes #972 (closed)
This is an updated version of John Ralls’ patch.