Free the alternate signal stack when thread / process stops, continued

Make sure caml_terminate_signals is called if caml_raise goes straight
to caml_fatal_uncaught_exception.

Refactoring: add dummy definitions of caml_init_signals and
caml_terminate_signals to the bytecode runtime system, so that no
caml_stop_stack_overflow_detection.

runtime/caml/signals.h

@@ -89,10 +89,8 @@ value caml_process_pending_actions_with_root_exn (value extra_root);
 int caml_set_signal_action(int signo, int action);
 CAMLextern int caml_setup_stack_overflow_detection(void);
 CAMLextern int caml_stop_stack_overflow_detection(void);
-#ifdef NATIVE_CODE
 CAMLextern void caml_init_signals(void);
 CAMLextern void caml_terminate_signals(void);
-#endif
 CAMLextern void (*caml_enter_blocking_section_hook)(void);
 CAMLextern void (*caml_leave_blocking_section_hook)(void);
 #ifdef POSIX_SIGNALS

runtime/fail_nat.c

@@ -31,6 +31,7 @@
 #include "caml/stack.h"
 #include "caml/roots.h"
 #include "caml/callback.h"
+#include "caml/signals.h"
 
 /* The globals holding predefined exceptions */
 
@@ -70,7 +71,10 @@ void caml_raise(value v)
   if (Is_exception_result(v))
     v = Extract_exception(v);
 
-  if (Caml_state->exception_pointer == NULL) caml_fatal_uncaught_exception(v);
+  if (Caml_state->exception_pointer == NULL) {
+    caml_terminate_signals();
+    caml_fatal_uncaught_exception(v);
+  }
 
   while (Caml_state->local_roots != NULL &&
          (char *) Caml_state->local_roots < Caml_state->exception_pointer) {

runtime/signals_byt.c

@@ -83,3 +83,5 @@ int caml_set_signal_action(int signo, int action)
 
 CAMLexport int caml_setup_stack_overflow_detection(void) { return 0; }
 CAMLexport int caml_stop_stack_overflow_detection(void) { return 0; }
+CAMLexport void caml_init_signals(void) { }
+CAMLexport void caml_terminate_signals(void) { }

runtime/sys.c

@@ -159,9 +159,7 @@ CAMLexport void caml_do_exit(int retcode)
 #ifdef _WIN32
   caml_restore_win32_terminal();
 #endif
-#ifdef NATIVE_CODE
   caml_terminate_signals();
-#endif
 #ifdef NAKED_POINTERS_CHECKER
   if (retcode == 0 && caml_naked_pointers_detected) {
     fprintf (stderr, "\nOut-of-heap pointers were detected by the runtime.\n"