Add a test for libatomic_ops minimal version required (at compile time).
Merge symbian branch to master.
-Merge useful code (if any) from mono_libgc branch.
+
+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).
+
+Declare GC_abort with noreturn attribute.
windows-untested: Remove if CMake can generate MS Visual Studio 6.0, 7.0, 8.0
project files.