ext/json/parser/parser.h: Add fallback MAYBE_UNUSED
https://github.com/flori/json/commit/e2ad91fc2094d3cc2f76adc6c55d420cd06f34d8
ext/json/parser/parser.h: Add fallback MAYBE_UNUSED
https://github.com/flori/json/commit/e2ad91fc2094d3cc2f76adc6c55d420cd06f34d8