build: fix failures with -Wcast-align and -Werror

Closes #457

lib/connect.c

@@ -619,7 +619,7 @@ static bool getaddressinfo(struct sockaddr* sa, char* addr,
 
   switch (sa->sa_family) {
     case AF_INET:
-      si = (struct sockaddr_in*) sa;
+      si = (struct sockaddr_in*)(void*) sa;
       if(Curl_inet_ntop(sa->sa_family, &si->sin_addr,
                         addr, MAX_IPADR_LEN)) {
         us_port = ntohs(si->sin_port);
@@ -629,7 +629,7 @@ static bool getaddressinfo(struct sockaddr* sa, char* addr,
       break;
 #ifdef ENABLE_IPV6
     case AF_INET6:
-      si6 = (struct sockaddr_in6*)sa;
+      si6 = (struct sockaddr_in6*)(void*) sa;
       if(Curl_inet_ntop(sa->sa_family, &si6->sin6_addr,
                         addr, MAX_IPADR_LEN)) {
         us_port = ntohs(si6->sin6_port);

lib/formdata.c

@@ -538,7 +538,7 @@ CURLFORMcode FormAdd(struct curl_httppost **httppost,
         /* this "cast increases required alignment of target type" but
            we consider it OK anyway */
         struct curl_slist* list = array_state?
-          (struct curl_slist*)array_value:
+          (struct curl_slist*)(void*)array_value:
           va_arg(params, struct curl_slist*);
 
         if(current_form->contentheader)

lib/if2ip.c

@@ -68,7 +68,7 @@ unsigned int Curl_ipv6_scope(const struct sockaddr *sa)
   (void) sa;
 #else
   if(sa->sa_family == AF_INET6) {
-    const struct sockaddr_in6 * sa6 = (const struct sockaddr_in6 *) sa;
+    const struct sockaddr_in6 * sa6 = (const struct sockaddr_in6 *)(void *) sa;
     const unsigned char * b = sa6->sin6_addr.s6_addr;
     unsigned short w = (unsigned short) ((b[0] << 8) | b[1]);
 
@@ -152,11 +152,12 @@ if2ip_result_t Curl_if2ip(int af, unsigned int remote_scope,
                 continue;
               }
 
-              addr = &((struct sockaddr_in6 *)iface->ifa_addr)->sin6_addr;
+              addr =
+                &((struct sockaddr_in6 *)(void *)iface->ifa_addr)->sin6_addr;
 #ifdef HAVE_SOCKADDR_IN6_SIN6_SCOPE_ID
               /* Include the scope of this interface as part of the address */
-              scopeid =
-                ((struct sockaddr_in6 *)iface->ifa_addr)->sin6_scope_id;
+              scopeid = ((struct sockaddr_in6 *)(void *)iface->ifa_addr)
+                            ->sin6_scope_id;
 
               /* If given, scope id should match. */
               if(remote_scope_id && scopeid != remote_scope_id) {
@@ -171,7 +172,8 @@ if2ip_result_t Curl_if2ip(int af, unsigned int remote_scope,
             }
             else
 #endif
-              addr = &((struct sockaddr_in *)iface->ifa_addr)->sin_addr;
+              addr =
+                  &((struct sockaddr_in *)(void *)iface->ifa_addr)->sin_addr;
             res = IF2IP_FOUND;
             ip = (char *) Curl_inet_ntop(af, addr, ipstr, sizeof(ipstr));
             snprintf(buf, buf_size, "%s%s", ip, scope);

lib/socks.c

@@ -603,7 +603,7 @@ CURLcode Curl_SOCKS5(const char *proxy_name,
       if(hp->ai_family == AF_INET) {
         socksreq[len++] = 1; /* ATYP: IPv4 = 1 */
 
-        saddr_in = (struct sockaddr_in*)hp->ai_addr;
+        saddr_in = (struct sockaddr_in*)(void*)hp->ai_addr;
         for(i = 0; i < 4; i++) {
           socksreq[len++] = ((unsigned char*)&saddr_in->sin_addr.s_addr)[i];
           infof(data, "%d\n", socksreq[len-1]);
@@ -613,7 +613,7 @@ CURLcode Curl_SOCKS5(const char *proxy_name,
       else if(hp->ai_family == AF_INET6) {
         socksreq[len++] = 4; /* ATYP: IPv6 = 4 */
 
-        saddr_in6 = (struct sockaddr_in6*)hp->ai_addr;
+        saddr_in6 = (struct sockaddr_in6*)(void*)hp->ai_addr;
         for(i = 0; i < 16; i++) {
           socksreq[len++] = ((unsigned char*)&saddr_in6->sin6_addr.s6_addr)[i];
         }