Fix typo in comment of signalObjectAndWait_func (Win32)

* win32_threads.c (signalObjectAndWait_func): Fix a typo in comment.
Improve debug-only messages of add/remove_roots and init_linux_data_start

* mark_rts.c (GC_add_roots_inner, GC_remove_root_at_pos): Log r_tmp
value (only if DEBUG_ADD_DEL_ROOTS).
* os_dep.c (GC_init_linux_data_start): Log unresolved [__]data_start
symbol (only if DEBUG_ADD_DEL_ROOTS and LINUX).