Fix -Wexpansion-to-defined warnings

Closes wahern#25

src/dns.c

@@ -203,10 +203,11 @@
 #endif
 
 #ifndef HAVE_STATIC_ASSERT
-#if DNS_GNUC_PREREQ(0,0,0) && !DNS_GNUC_PREREQ(4,6,0)
-#define HAVE_STATIC_ASSERT 0 /* glibc doesn't check GCC version */
+#if (defined static_assert) && \
+	(!DNS_GNUC_PREREQ(0,0,0) || DNS_GNUC_PREREQ(4,6,0)) /* glibc doesn't check GCC version */
+#define HAVE_STATIC_ASSERT 1
 #else
-#define HAVE_STATIC_ASSERT (defined static_assert)
+#define HAVE_STATIC_ASSERT 0
 #endif
 #endif
 
@@ -372,7 +373,11 @@ const char *dns_strerror(int error) {
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
 #ifndef HAVE___ATOMIC_FETCH_ADD
-#define HAVE___ATOMIC_FETCH_ADD (defined __ATOMIC_RELAXED)
+#ifdef __ATOMIC_RELAXED
+#define HAVE___ATOMIC_FETCH_ADD 1
+#else
+#define HAVE___ATOMIC_FETCH_ADD 0
+#endif
 #endif
 
 #ifndef HAVE___ATOMIC_FETCH_SUB
@@ -779,7 +784,11 @@ DNS_NOTUSED static size_t dns_strnlcpy(char *dst, size_t lim, const char *src, s
 } /* dns_strnlcpy() */
 
 
-#define DNS_HAVE_SOCKADDR_UN (defined AF_UNIX && !defined _WIN32)
+#if (defined AF_UNIX && !defined _WIN32)
+#define DNS_HAVE_SOCKADDR_UN 1
+#else
+#define DNS_HAVE_SOCKADDR_UN 0
+#endif
 
 static size_t dns_af_len(int af) {
 	static const size_t table[AF_MAX]	= {
@@ -6114,11 +6123,19 @@ static void dns_socketclose(int *fd, const struct dns_options *opts) {
 #endif
 
 #ifndef HAVE_SOCK_CLOEXEC
-#define HAVE_SOCK_CLOEXEC (defined SOCK_CLOEXEC)
+#ifdef SOCK_CLOEXEC
+#define HAVE_SOCK_CLOEXEC 1
+#else
+#define HAVE_SOCK_CLOEXEC 0
+#endif
 #endif
 
 #ifndef HAVE_SOCK_NONBLOCK
-#define HAVE_SOCK_NONBLOCK (defined SOCK_NONBLOCK)
+#ifdef SOCK_NONBLOCK
+#define HAVE_SOCK_NONBLOCK 1
+#else
+#define HAVE_SOCK_NONBLOCK 0
+#endif
 #endif
 
 #define DNS_SO_MAXTRY	7