build: adjust clang-tidy warning exclusion logic

Enable all clang-tidy warnings by default instead of disabling them.
This ensures that we don't miss useful warnings on each clang-tidy
version upgrade. A drawback of this is that it will force us to either
fix or adjust the warnings as soon as possible.

src/nvim/main.c

@@ -343,7 +343,7 @@ int main(int argc, char **argv)
   // Don't redraw until much later.
   RedrawingDisabled++;
 
-  setbuf(stdout, NULL);
+  setbuf(stdout, NULL);  // NOLINT(bugprone-unsafe-functions)
 
   full_screen = !silent_mode;