fix: backport treesit-available-p sooner

This fixes Doom for Emacs 27-28 users (or builds without treesit).

lisp/doom-compat.el

@@ -132,6 +132,25 @@ The functions in the hook are called with one parameter -- the
       (funcall fn theme)
       (run-hook-with-args 'enable-theme-functions theme))))
 
+;; Introduced in 29.1
+;; In case of Emacs builds where treesit isn't built in (to avoid void-function
+;; errors and verbose, redundant checks everywhere).
+;;;###autodef
+(unless (fboundp 'treesit-available-p)
+  (defun treesit-available-p ()
+    "Return non-nil if tree-sitter support is built-in and available."
+    nil))
+
+;;;###autoload
+(unless (fboundp 'treesit-library-abi-version)
+  (defun treesit-library-abi-version (&optional _min-compatible)
+    0))
+
+;;;###autoload
+(unless (fboundp 'treesit-language-abi-version)
+  (defun treesit-language-abi-version (&optional _lang)
+    nil))
+
 
 ;;; From Emacs >= 30
 ;; Introduced in 30.1