libc: Fix dns-related build issues.

libc: Fix dns-related build issues.

- The first observed issue is linking failure:
`
/usr/bin/ld: libc/libc_so.a(encodeq.os): in function `__encode_question':
encodeq.c:(.text+0x16): undefined reference to `__GI___dn_comp'
/usr/bin/ld: libc/libc_so.a(dnslookup.os): in function `__dns_lookup':
dnslookup.c:(.text+0x6fb): undefined reference to `__GI___dn_expand'
/usr/bin/ld: dnslookup.c:(.text+0x7ab): undefined reference to `__hnbad'
collect2: error: ld returned 1 exit status
`
The root cause is that the resolv.c file contains
some functions (dn_comp, dn_expand, __hnbad)
under `#ifdef L_ns_name` and `#ifdef L_ns_comp`
which wasn't defined, so we had undefined refs to such functions.

- The second issue is misleading indentation inside `ns_name_pack`.
`
libc/inet/resolv.c: In function '__ns_name_pack':
libc/inet/resolv.c:3519:17: warning: this 'if' clause does not guard...
 3519 |                 if (msg != NULL)
...
./include/errno.h:73:18: note: ...this statement, but the latter
is misleadingly indented as if it were guarded by the 'if'
   73 | #   define errno errno             /* For #ifndef errno tests.  */
      |                  ^~~~~
libc/inet/resolv.c:3522:25: note: in expansion of macro 'errno'
 3522 |                         errno = EMSGSIZE;
`

Signed-off-by: Dmitry Chestnykh <dm.chestnykh@gmail.com>