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.

modules/regex/SCsub

@@ -6,12 +6,10 @@ Import('env_modules')
 env_regex = env_modules.Clone()
 
 if env['builtin_pcre2']:
-    jit_blacklist = ['javascript', 'uwp']
-
     thirdparty_dir = '#thirdparty/pcre2/src/'
     thirdparty_flags = ['PCRE2_STATIC', 'HAVE_CONFIG_H']
 
-    if 'platform' in env and env['platform'] not in jit_blacklist:
+    if env['builtin_pcre2_with_jit']:
         thirdparty_flags.append('SUPPORT_JIT')
 
     thirdparty_sources = [