increase TTY_NAME_MAX limit to 32

the old value of 20 was reported by Laurent Bercot as being
insufficient for a reasonable real-world usage case. actual problem
was the internal buffer used by ttyname(), but the implementation of
ttyname uses TTY_NAME_MAX, and for consistency it's best to increase
both. the new value is aligned with glibc.

include/limits.h

@@ -55,7 +55,7 @@
 #define WORD_BIT 32
 #define SSIZE_MAX LONG_MAX
 #define TZNAME_MAX 6
-#define TTY_NAME_MAX 20
+#define TTY_NAME_MAX 32
 #define HOST_NAME_MAX 255
 
 /* Implementation choices... */