macOS's newlocale() does not follow POSIX specification - it doesn't
reuse the passed locale_t, causing ~1,472 bytes leak per json_tokener_parse() call.
This is the same issue as #668 (FreeBSD). The existing workaround works,
but macOS was not auto-detected.
Tested with AddressSanitizer: leak drops from 1,472,000 bytes to ~120 bytes
(system init only).
