Fix ptsname(3) and ttyname(3) to use TLS.

Be safe by default.

Change-Id: I6c4a3f1fd4eee3a651b3162ce95b7e873de57521
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index 3053e85..dfb788e 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -131,7 +131,7 @@
 int getpt(void);
 int grantpt(int);
 int posix_openpt(int);
-char* ptsname(int) __warnattr("ptsname is not thread-safe; use ptsname_r instead");
+char* ptsname(int);
 int ptsname_r(int, char*, size_t);
 int unlockpt(int);