thread_pthread.c: Use `getpagesize()` when `pthread_attr_getguardsize` is unavailable

This is also for emscripten.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62409 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.ac

@@ -2290,7 +2290,7 @@ AS_IF([test x"$enable_pthread" = xyes], [
 	AC_DEFINE(NON_SCALAR_THREAD_ID)
     ])
     AC_CHECK_FUNCS(sched_yield pthread_attr_setinheritsched \
-	pthread_attr_get_np pthread_attr_getstack \
+	pthread_attr_get_np pthread_attr_getstack pthread_attr_getguardsize \
 	pthread_get_stackaddr_np pthread_get_stacksize_np \
 	thr_stksegment pthread_stackseg_np pthread_getthrds_np \
 	pthread_condattr_setclock \

thread_pthread.c

@@ -561,8 +561,12 @@ get_stack(void **addr, size_t *size)
     CHECK_ERR(pthread_attr_getstackaddr(&attr, addr));
     CHECK_ERR(pthread_attr_getstacksize(&attr, size));
 # endif
+# ifdef HAVE_PTHREAD_ATTR_GETGUARDSIZE
     CHECK_ERR(pthread_attr_getguardsize(&attr, &guard));
     *size -= guard;
+# else
+    *size -= getpagesize();
+# endif
     pthread_attr_destroy(&attr);
 #elif defined HAVE_PTHREAD_ATTR_GET_NP /* FreeBSD, DragonFly BSD, NetBSD */
     pthread_attr_t attr;