Add "isolate" argument to LOG macro to avoid TLS fetches.

src/platform-openbsd.cc

Index: src/platform-openbsd.cc
diff --git a/src/platform-openbsd.cc b/src/platform-openbsd.cc
index 03f5620a2d318296e729f245eb0c7c73eb6237de..568acdbae868eb508508cd80ff1e40deb8c7c7d4 100644
--- a/src/platform-openbsd.cc
+++ b/src/platform-openbsd.cc
@@ -154,7 +154,7 @@ void* OS::Allocate(const size_t requested,
   void* mbase = mmap(NULL, msize, prot, MAP_PRIVATE | MAP_ANON, -1, 0);
 
   if (mbase == MAP_FAILED) {
-    LOG(StringEvent("OS::Allocate", "mmap failed"));
+    LOG(ISOLATE, StringEvent("OS::Allocate", "mmap failed"));
     return NULL;
   }
   *allocated = msize;