Merge symbian branch to master.
-Merge useful code (if any) from mono_libgc branch (e.g., FALLBACK_TO_MMAP,
-SIGTSTP/SIGCONT on freebsd/amd64, GC_thread_is_registered, do not abort on
-SuspendThread failure, GC_DllMain, &GC_thread_key+sizeof fix for gcc-3,
-reserve errno in GC_restart_handler, assert DATASTART in
-GC_register_data_segments, assert result HBLKSIZE-aligned in
-GC_unix_mmap_get_mem, GC_DONT_REGISTER_MAIN_STATIC_DATA, last_fo_entries and
-last_words_finalized in GC_collect_or_expand, ignore thread_info/resume
-errors in GC_thread_resume, add GC_on_heap_resize).
+Merge useful code (if any) from mono_libgc branch (e.g.,
+do not abort on SuspendThread failure,
+last_fo_entries and last_words_finalized in GC_collect_or_expand,
+ignore thread_info/resume errors in GC_thread_resume,
+GC_on_heap_resize).
Declare GC_abort with noreturn attribute.