In libobjc/: Implemented objc_sync_enter() and objc_sync_exit(), which are required by @synchronized() to work.

In libobjc/:
       Implemented objc_sync_enter() and objc_sync_exit(), which are
       required by @synchronized() to work.
       * objc-sync.c: New file.
       * objc/objc-sync.h: New file.
       * objc-private/objc-sync.h: New file.
       * init.c (__objc_exec_class): Call __objc_sync_init() during the
       Objective-C runtime startup.
       * Makefile.in: Added objc-sync.c and objc-sync.h.
       * configure.ac: Added GCC_CHECK_TLS.
       * acinclude.m4: Include ../config/enable.m4 and ../config/tls.m4.
       * configure: Regenerated.
       * config.h.in: Regenerated.

From-SVN: r164276