core: Follow up to r1897240: Opt-out for AP_HAS_THREAD_LOCAL and/or pcre's usage.

core: Follow up to r1897240: Opt-out for AP_HAS_THREAD_LOCAL and/or pcre's usage.

If the compiler's thread_local is not efficient enough on some platforms, or
not desired, have a way to disable its usage in httpd (at compile time).

Handle -DAP_NO_THREAD_LOCAL and/or -DAPREG_NO_THREAD_LOCAL as build opt-out for
thread_local usage in httpd gobally and/or in ap_regex only (respectively).

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1897689 13f79535-47bb-0310-9956-ffa450edef68