add CLOEXEC to various DNS related code

Occasionally file descriptors seem to be leaking across execs
from DNS related calls. Set close-on-execute for the various
sockets / file to prevent file descriptor leakage.

Change-Id: I4724b47bc7236f40c29518a6075598a9bba48b0a
diff --git a/libc/dns/resolv/res_send.c b/libc/dns/resolv/res_send.c
index 9b36f55..b6a990a 100644
--- a/libc/dns/resolv/res_send.c
+++ b/libc/dns/resolv/res_send.c
@@ -779,7 +779,7 @@
 		if (statp->_vcsock >= 0)
 			res_nclose(statp);
 
-		statp->_vcsock = socket(nsap->sa_family, SOCK_STREAM, 0);
+		statp->_vcsock = socket(nsap->sa_family, SOCK_STREAM | SOCK_CLOEXEC, 0);
 		if (statp->_vcsock > highestFD) {
 			res_nclose(statp);
 			errno = ENOTSOCK;
@@ -1062,7 +1062,7 @@
 	nsap = get_nsaddr(statp, (size_t)ns);
 	nsaplen = get_salen(nsap);
 	if (EXT(statp).nssocks[ns] == -1) {
-		EXT(statp).nssocks[ns] = socket(nsap->sa_family, SOCK_DGRAM, 0);
+		EXT(statp).nssocks[ns] = socket(nsap->sa_family, SOCK_DGRAM | SOCK_CLOEXEC, 0);
 		if (EXT(statp).nssocks[ns] > highestFD) {
 			res_nclose(statp);
 			errno = ENOTSOCK;