chore: add additional compiler flags (#17815)

Added:
  - -Wdouble-promotion
  - -Wmissing-noreturn
  - -Wmissing-format-attribute
  - -Wsuggest-attribute={pure,const,malloc,cold}

Resolves: #343

src/nvim/ui_client.c

@@ -87,6 +87,7 @@ Object ui_client_handle_redraw(uint64_t channel_id, Array args, Error *error)
 ///
 /// This is just a stub. the full version will handle input, resizing, etc
 void ui_client_execute(uint64_t chan)
+  FUNC_ATTR_NORETURN
 {
   while (true) {
     loop_poll_events(&main_loop, -1);