Bug 1364573 - Don't relazify class default constructors.

Because of the wacko way we handle toString offsets for class default constructors, those offsets cannot be recovered if we relazify the functions.
Luckily there's no reason to relazify them, their JSScripts are very small: either a single 'retrval' for non-derived, and still fairly small for derived.

js/src/jsscript.h

@@ -1494,6 +1494,7 @@ class JSScript : public js::gc::TenuredCell
     bool isRelazifiable() const {
         return (selfHosted() || lazyScript) && !hasInnerFunctions_ && !types_ &&
                !isGenerator() && !hasBaselineScript() && !hasAnyIonScript() &&
+               !isDefaultClassConstructor() &&
                !doNotRelazify_;
     }
     void setLazyScript(js::LazyScript* lazy) {