fix: lexical-binding warnings at startup on 30+

A check was added on some recent commit of Emacs 30, where a warning
popup is emitted on any file lacking a lexical-binding setting in the
file's mode line, like these files.

Author: hlissner

Diff for: c++-mode/.yas-setup.el

@@ -1,3 +1,5 @@
+;; -*- lexical-binding: t -*-
+
 (defun doom-snippets-c++-using-std-p ()
   "Return non-nil if 'using namespace std' is found at the top of this file."
   (save-excursion

Diff for: doom-snippets.el

@@ -1,4 +1,4 @@
-;;; doom-snippets.el --- A collection of yasnippet snippets
+;;; doom-snippets.el --- A collection of yasnippet snippets -*- lexical-binding: t -*-
 ;;
 ;; Copyright (C) 2017-2024 Henrik Lissner
 ;;

Diff for: emacs-lisp-mode/.yas-setup.el

@@ -1,4 +1,4 @@
-;;; emacs-lisp-mode/.yas-setup.el
+;;; emacs-lisp-mode/.yas-setup.el -*- no-byte-compile: t; lexical-binding: t -*-
 
 (defvar doom-modules-dir)
 

Diff for: fundamental-mode/.yas-setup.el

@@ -1,2 +1,2 @@
-;; -*- no-byte-compile: t; -*-
+;; -*- no-byte-compile: t; lexical-binding: t; -*-
 (require 'doom-snippets-lib)

Diff for: prog-mode/.yas-setup.el

@@ -1,4 +1,4 @@
-;; -*- no-byte-compile: t; -*-
+;; -*- no-byte-compile: t; lexical-binding: t; -*-
 
 (require 'yasnippet)
 
@@ -34,4 +34,4 @@
 Otherwise the reversed output of function `yas-trimmed-comment-start' is returned."
   (if (eq (length comment-end) 0)
       (yas-string-reverse (yas-trimmed-comment-start))
-    (yas-s-trim comment-end)))
+    (yas-s-trim comment-end)))

Diff for: python-mode/.yas-setup.el

@@ -1,4 +1,4 @@
-;; -*- no-byte-compile: t; -*-
+;; -*- no-byte-compile: t; lexical-binding: t -*-
 
 (defun python-split-args (arg-string)
   "Split a python argument string into ((name, default)..) tuples"