add more C89-like targets; fix related stuff

src/dash.c

@@ -167,9 +167,11 @@ static size_t mg_dash_print_endpoint(mg_pfn_t fn, void *arg, va_list *ap) {
 void mg_dash_send_change(struct mg_mgr *mgr, struct mg_field_set *set) {
   struct mg_connection *c;
   for (c = mgr->conns; c != NULL; c = c->next) {
-    struct mg_dash_cdata *d = (struct mg_dash_cdata *) c->data;
-    struct mg_dash_user *u = d->u;
+    struct mg_dash_cdata *d;
+    struct mg_dash_user *u;
     if (!c->is_websocket) continue;
+    d = (struct mg_dash_cdata *) c->data;
+    u = d->u;
     if (u == NULL) continue;
     if (set->index != NULL && *set->index < 0) {
       int sz = mg_dash_array_size(set, u);

src/net_builtin.c

@@ -972,7 +972,7 @@ static void rx_ndp_ra(struct mg_tcpip_if *ifp, struct pkt *pkt) {
   bool gotl2addr = false, gotprefix = false, changed = false;
   uint8_t l2[sizeof(struct mg_l2addr)];
   uint32_t mtu = 0;
-  uint8_t *prefix, prefix_len;
+  uint8_t *prefix = NULL, prefix_len = 0;
 
   if (pkt->pay.len < sizeof(*ra)) return;
   if (ifp->state6 == MG_TCPIP_STATE_UP) {

src/tls_chacha20.c

@@ -7,7 +7,7 @@
 #include "tls_chacha20.h"
 #include "tls.h"
 
-#if MG_TLS == MG_TLS_BUILTIN
+#if MG_TLS == MG_TLS_BUILTIN && MG_ENABLE_CHACHA20
 // ******* BEGIN: chacha-portable/chacha-portable.h ********
 
 #if !defined(__cplusplus) && !defined(_MSC_VER) && \

src/tls_chacha20.h

@@ -8,7 +8,7 @@
 #include "config.h"
 #include "tls.h"
 
-#if MG_TLS == MG_TLS_BUILTIN
+#if MG_TLS == MG_TLS_BUILTIN && MG_ENABLE_CHACHA20
 #ifndef __PORTABLE_8439_H
 #define __PORTABLE_8439_H
 #if defined(__cplusplus)