Move mtctxres.c to libc_dns.a.

Has the effect of making ___mtctxres hidden.

Bug: 11156955
Change-Id: I5aa5f49344ad5ecb33f48737430561b329bcbb0d
(cherry picked from commit 891ec7a6e46e60d7dfa1cf229e14a8e8634e272b)
1 file changed