Merge pull request #39995 from 3405691582/BuildfixStackBounds

[stdlib] Buildfix getting stack bounds on OpenBSD.

Author: lorentey

stdlib/public/stubs/Stubs.cpp

@@ -532,10 +532,19 @@ __swift_bool _swift_stdlib_getCurrentStackBounds(__swift_uintptr_t *outBegin,
   *outEnd = highLimit;
   return true;
 
-#elif defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__ANDROID__) || defined(__linux__)
+#elif defined(__OpenBSD__)
+  stack_t sinfo;
+  if (pthread_stackseg_np(pthread_self(), &sinfo) != 0) {
+    return false;
+  }
+
+  *outBegin = (uintptr_t)sinfo.ss_sp - sinfo.ss_size;
+  *outEnd = (uintptr_t)sinfo.ss_sp;
+  return true;
+#elif defined(__FreeBSD__) || defined(__ANDROID__) || defined(__linux__)
   pthread_attr_t attr;
 
-#if defined(__FreeBSD__) || defined(__OpenBSD__)
+#if defined(__FreeBSD__)
   if (0 != pthread_attr_init(&attr) || 0 != pthread_attr_get_np(pthread_self(), &attr)) {
     return false;
   }