runtime: correct _stdlib_thread_key_create

The mapping of the return value of the `FlsAlloc` was flipped resulting
in the failure of the TLS key creation.  The test suite would fail to
generate the TLS key resulting in failures.

stdlib/public/stubs/ThreadLocalStorage.cpp

@@ -43,7 +43,9 @@ static inline int
 _stdlib_thread_key_create(__swift_thread_key_t * _Nonnull key,
                           __swift_thread_key_destructor _Nullable destructor) {
   *key = FlsAlloc(destroyTLS_CCAdjustmentThunk);
-  return *key != FLS_OUT_OF_INDEXES;
+  if (*key == FLS_OUT_OF_INDEXES)
+    return GetLastError();
+  return 0;
 }
 
 #endif