runtime: make out-of-memory failures fatal

Match the Go runtime by terminating instead of unwinding when an
allocator exhausts the heap. Recovering an OOM can leave allocator locks
held and cannot safely continue when the panic path itself needs memory.

src/runtime/gc_leaking.go

@@ -53,7 +53,7 @@ func alloc(size uintptr, layout unsafe.Pointer) unsafe.Pointer {
 			continue
 		}
 		// Failed to make the heap bigger, so we must really be out of memory.
-		runtimePanic("out of memory")
+		runtimeFatal("out of memory")
 	}
 	gcLock.Unlock()