libc should use O_CLOEXEC when opening files for its own use.

Change-Id: I159f1d57e0ca090d837f57854fcef5879b8b8248
diff --git a/libc/dns/resolv/res_cache.c b/libc/dns/resolv/res_cache.c
index 77a1b4d..0201aa8 100644
--- a/libc/dns/resolv/res_cache.c
+++ b/libc/dns/resolv/res_cache.c
@@ -1436,7 +1436,7 @@
     char* buf;
     int fileLen;
 
-    fp = fopen("/data/reslog.txt", "w+");
+    fp = fopen("/data/reslog.txt", "w+e");
     if (fp != NULL) {
         statep = __res_get_state();