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

Be safe by default.

Change-Id: I6c4a3f1fd4eee3a651b3162ce95b7e873de57521

libc/include/stdlib.h

@@ -131,7 +131,7 @@ void srandom(unsigned int);
 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);