Add ReleaseStore function on OpenBSD.

Review URL: http://codereview.chromium.org/2916001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5036 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/platform-openbsd.cc

@@ -83,6 +83,12 @@ void OS::Setup() {
 }
 
 
+void OS::ReleaseStore(volatile AtomicWord* ptr, AtomicWord value) {
+  __asm__ __volatile__("" : : : "memory");
+  *ptr = value;
+}
+
+
 uint64_t OS::CpuFeaturesImpliedByPlatform() {
   return 0;  // OpenBSD runs on anything.
 }