Fix CreateTableSpace() so it will compile without HAVE_SYMLINK.

This has been broken since 9.3 (commit 82b1b213cad3a69c to be exact),
which suggests that nobody is any longer using a Windows build system that
doesn't provide a symlink emulation.  Still, it's wrong on its own terms,
so repair.

YUriy Zhuravlev

src/backend/commands/tablespace.c

@@ -366,13 +366,14 @@ CreateTableSpace(CreateTableSpaceStmt *stmt)
 
 	/* We keep the lock on pg_tablespace until commit */
 	heap_close(rel, NoLock);
+
+	return tablespaceoid;
 #else							/* !HAVE_SYMLINK */
 	ereport(ERROR,
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 			 errmsg("tablespaces are not supported on this platform")));
+	return InvalidOid;			/* keep compiler quiet */
 #endif   /* HAVE_SYMLINK */
-
-	return tablespaceoid;
 }
 
 /*