docs: enable more compiler warnings for C snippets, fix 3 finds

Also:
- sync gcc option order.
- unfold lines in C snippet.

Closes #21006

docs/libcurl/curl_mime_data_cb.md

@@ -121,7 +121,7 @@ struct ctl {
 size_t read_callback(char *buffer, size_t size, size_t nitems, void *arg)
 {
   struct ctl *p = (struct ctl *)arg;
-  curl_off_t sz = p->size - p->position;
+  size_t sz = (size_t)(p->size - p->position);
 
   nitems *= size;
   if(sz > nitems)

docs/libcurl/curl_ws_recv.md

@@ -97,7 +97,7 @@ int main(void)
     if(result == CURLE_OK) {
       if(meta->bytesleft == 0)
         break; /* finished receiving */
-      if(meta->bytesleft > sizeof(buffer) - offset)
+      if(meta->bytesleft > (curl_off_t)(sizeof(buffer) - offset))
         result = CURLE_TOO_LARGE;
     }
 

docs/libcurl/opts/CURLOPT_DEBUGFUNCTION.md

@@ -111,9 +111,8 @@ NULL
 # EXAMPLE
 
 ~~~c
-static
-void dump(const char *text,
-          FILE *stream, unsigned char *ptr, size_t size)
+static void dump(const char *text,
+                 FILE *stream, unsigned char *ptr, size_t size)
 {
   size_t i;
   size_t c;
@@ -143,10 +142,9 @@ void dump(const char *text,
   }
 }
 
-static
-int my_trace(CURL *handle, curl_infotype type,
-             char *data, size_t size,
-             void *clientp)
+static int my_trace(CURL *handle, curl_infotype type,
+                    char *data, size_t size,
+                    void *clientp)
 {
   const char *text;
   (void)handle;
@@ -156,6 +154,7 @@ int my_trace(CURL *handle, curl_infotype type,
   case CURLINFO_TEXT:
     fputs("== Info: ", stderr);
     fwrite(data, size, 1, stderr);
+    return 0;
   default: /* in case a new one is introduced to shock us */
     return 0;