Mac build fails with glib.h static assertion
On macOS, cargo's compilation of the C bindings seems to be either i386 or dual-arch x86_64+i386, triggering a static assert failure in glib.h on the i386 side.
This is a known incompatibility between Mac i386 and recent versions of glib, which refuses to compile if long long doesn't match guint64's size... but there's no obvious reason we should be building for the obsolete i386 target anyway (normally clang gives you 64-bit output),
As a workaround running
ARCHFLAGS="-arch x86_64" make forces a 64-bit only build, which is what we want anyway and actually works, but a cleaner solution would be nice without adding hacks to the build directions.
Not yet quite sure where the i386 is coming from or how to fix it properly.