Bug 702426: Add test.

js/src/jit-test/tests/basic/bug702426-regexp-gc.js

@@ -0,0 +1,5 @@
+function g(code) {
+    eval("(function(){" + code + "})")()
+}
+g("evalcx(\"(/a/g,function(){})\")");
+g("'a'.replace(/a/g,gc)")