assorted fixes for musl

--- a/src/include/spf_dns.h
+++ a/src/include/spf_dns.h
@@ -99,11 +99,13 @@
  */
 
 #if !defined(HAVE_NETDB_H) && !defined(_WIN32)
-#define NETDB_SUCCESS	0
 #define	HOST_NOT_FOUND 	1		/**< NXDOMAIN (authoritative answer)*/
 #define	TRY_AGAIN		2		/**< SERVFAIL (no authoritative answer)*/
 #define	NO_RECOVERY		3		/**< invalid/unimplmeneted query	*/
 #define	NO_DATA			4		/**< host found, but no RR of req type*/
+#endif
+#ifndef NETDB_SUCCESS
+#define NETDB_SUCCESS	0
 #endif
 typedef int SPF_dns_stat_t;
 
--- a/src/libspf2/spf_dns_resolv.c
+++ b/src/libspf2/spf_dns_resolv.c
@@ -606,7 +606,7 @@ SPF_dns_resolv_free(SPF_dns_server_t *spf_dns_server)
 {
 	SPF_ASSERT_NOTNULL(spf_dns_server);
 
-#if ! HAVE_DECL_RES_NINIT
+#if ! HAVE_DECL_RES_NINIT && HAVE_RES_CLOSE
 	res_close();
 #endif