Fix phpGH-16851: JIT_G(enabled) not set correctly on other threads

There doesn't seem to be a thread post-startup hook that runs after
zend_startup_cb() that could be used for this

this fix is similar to accel_startup_ok() as seen here: https://github.com/php/php-src/blob/fc1db70f106525e81f9a24539340b7cf2e82e844/ext/opcache/ZendAccelerator.c#L2631-L2634

Closes phpGH-16853.

Author: dktapps

NEWS

@@ -27,6 +27,8 @@ PHP                                                                        NEWS
 - Opcache:
   . Fixed bug GH-16770 (Tracing JIT type mismatch when returning UNDEF).
     (nielsdos, Dmitry)
+  . Fixed bug GH-16851 (JIT_G(enabled) not set correctly on other threads).
+    (dktapps)
 
 - OpenSSL:
   . Prevent unexpected array entry conversion when reading key. (nielsdos)