Segregated suspend/restart signal init changes into their own branch.
Better handling in signal setter/getter of non-signal-using OSes.
Extend new suspend/restart signal macro redirection to other OSes beyond Linux.
Fixed typo in restart signal setter function name.
Replace SIG_THR_RESTART macro to a variable in pthread_stop_world

* pthread_stop_world.c (GC_sig_thr_restart): New STATIC variable
(only unless NaCl or OpenBSD) initialized to SIG_THR_RESTART.
* pthread_stop_world.c (GC_unblock_gc_signals,
GC_suspend_handler_inner, GC_restart_handler, GC_start_world,
GC_stop_init, GC_get_thr_restart_signal): Use GC_sig_thr_restart
instead of SIG_THR_RESTART (only unless NaCl or OpenBSD); update
comment.
Replace SIG_SUSPEND macro to a variable in pthread_stop_world

* misc.c (GC_get_suspend_signal): Define (as always returning -1) in
this file only if Darwin or Win32 threads.
* os_dep.c (GC_dirty_init): Replace SIG_SUSPEND with the value of
GC_get_suspend_signal() invocation.
* pthread_support.c (pthread_sigmask): Likewise.
* pthread_stop_world.c (GC_sig_suspend): New STATIC variable (only
unless NaCl or OpenBSD) initialized to SIG_SUSPEND.
* pthread_stop_world.c (GC_unblock_gc_signals,
GC_suspend_handler_inner, GC_suspend_all, GC_stop_init): Use
GC_sig_suspend instead of SIG_SUSPEND (only unless NaCl or OpenBSD);
update comment.
* pthread_stop_world.c (GC_get_suspend_signal): Define function (which
returns GC_sig_suspend if available).
Move GC_get_suspend/thr_restart_signal to misc.c for NaCl and OpenBSD

* misc.c (GC_get_suspend_signal, GC_get_thr_restart_signal): Define
also for OpenBSD and NaCl targets in this file (always returns -1).
* pthread_stop_world.c (GC_get_suspend_signal,
GC_get_thr_restart_signal): Move function definition up to the
definition of GC_sig_suspend and GC_sig_thr_restart variables (i.e.,
define function only if not OpenBSD and not NaCl target in this file).
Add thread suspend/resume signals public setters (POSIX threads)

* include/gc.h (GC_set_suspend_signal, GC_set_thr_restart_signal):
Add public function declaration (to specify non-default signals to
suspend/resume threads).
* include/gc.h (GC_get_suspend_signal, GC_get_thr_restart_signal):
Update comment.
* misc.c (GC_set_suspend_signal, GC_set_thr_restart_signal): Add
public no-op function (only for Darwin, OpenBSD, Win32 and NaCl).
* pthread_stop_world.c (GC_set_suspend_signal,
GC_set_thr_restart_signal): Add public setter to alter the default
signals used to suspend and resume threads (only if not OpenBSD or
NaCl); has no effect if GC is initialized.
Dummy merge remote-tracking branch 'jcbeaudoin/signals_init'
Merge branch 'add-signals-setters'
Recognize GC_SIG_SUSPEND and GC_SIG_THR_RESTART tuning macros in gc.h

* include/gc.h (GC_SIG_SUSPEND, GC_SIG_THR_RESTART): New micro
recognized to tune GC_INIT with the non-default signal to be used by
GC to suspend (and resume, respectively) threads (only if GC_THREADS).
* include/gc.h (GC_INIT_CONF_SUSPEND_SIGNAL,
GC_INIT_CONF_THR_RESTART_SIGNAL): New macro (used internally by
GC_INIT).
* include/gc.h (GC_INIT): Invoke GC_INIT_CONF_SUSPEND_SIGNAL and
GC_INIT_CONF_THR_RESTART_SIGNAL before GC_init().
Update ChangeLog file