pcre2: Use scons option to disable JIT on some platforms

Third-party platforms (e.g. console ports) need to be able to
disable JIT support in the regex module too, so it can't be
hardcoded in the module SCsub. This is cleaner this way anyway.

Fixes #19316.

platform/javascript/detect.py

@@ -24,6 +24,7 @@ def get_opts():
 def get_flags():
     return [
         ('tools', False),
+        ('builtin_pcre2_with_jit', False),
         # Disabling the mbedtls module reduces file size.
         # The module has little use due to the limited networking functionality
         # in this platform. For the available networking methods, the browser