Add JavaScriptCore support

JavaScriptCore is Apple's Javascript implementation and uses the now standard `globalThis` to expose the global variable. This adds sprintf to the global space for JavaScriptCore.

Author: pasamio

CONTRIBUTORS.md

@@ -22,5 +22,6 @@ Pablo [@ppollono](https://github.com/ppollono)
 Rabehaja Stevens [@RABEHAJA-STEVENS](https://github.com/RABEHAJA-STEVENS)
 Raphael Pigulla [@pigulla](https://github.com/pigulla)
 rebeccapeltz [@rebeccapeltz](https://github.com/rebeccapeltz)
+Sam Moffatt [@pasamio](https://github.com/pasamio)
 Stefan Tingström [@stingstrom](https://github.com/stingstrom)
 Tim Gates [@timgates42](https://github.com/timgates42)