disable GJS JIT

This BZ causes the JIT to crash: https://bugzilla.gnome.org/show_bug.cgi?id=616193

==11966== Process terminating with default action of signal 11 (SIGSEGV): dumping core
==11966==  Access not within mapped region at address 0xFEFFEE30
==11966==    at 0x402B710: ???
==11966==    by 0x95529E1: EnterBaseline(JSContext*, js::jit::EnterJitData&) [clone .part.192] (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x9553219: js::jit::EnterBaselineMethod(JSContext*, js::RunState&) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x92FF3F8: Interpret(JSContext*, js::RunState&) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x9300117: js::RunScript(JSContext*, js::RunState&) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x9300330: js::Execute(JSContext*, JS::Handle<JSScript*>, JSObject&, JS::Value*) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x93A8969: JS::Evaluate(JSContext*, JS::Handle<JSObject*>, JS::CompileOptions, unsigned short const*, unsigned long, JS::Value*) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x93A8ABD: JS::Evaluate(JSContext*, JS::Handle<JSObject*>, JS::CompileOptions, char const*, unsigned long, JS::Value*) (in /usr/lib/x86_64-linux-gnu/libmozjs-24.so.0.0.0)
==11966==    by 0x55D2CC5: gjs_eval_with_scope (in /usr/lib/libgjs.so.0.0.0)
==11966==    by 0x55CCCD2: gjs_context_eval (in /usr/lib/libgjs.so.0.0.0)
==11966==    by 0x55CCEAA: gjs_context_eval_file (in /usr/lib/libgjs.so.0.0.0)
==11966==    by 0x400EC2: test (test-all-js.c:60)

Signed-off-by: Adrian Negreanu <adrian.m.negreanu@intel.com>