Switch static-if checks to use boundp and fboundp

Resolves #263

Author: dgutov

diff-hl.el

@@ -421,7 +421,7 @@ It can be a relative expression as well, such as \"HEAD^\" with Git, or
   (or (memq state '(edited conflict))
       (and (eq state 'up-to-date)
            ;; VC state is stale in after-revert-hook.
-           (or (static-if (>= emacs-major-version 31)
+           (or (static-if (boundp 'revert-buffer-in-progress)
                    revert-buffer-in-progress
                  revert-buffer-in-progress-p)
                ;; Diffing against an older revision.
@@ -740,7 +740,7 @@ Return a list of line overlays used."
 (defun diff-hl--resolve (value-or-buffer cb)
   (if (listp value-or-buffer)
       (funcall cb value-or-buffer)
-    (static-if (>= emacs-major-version 31)
+    (static-if (fboundp 'vc-run-delayed-success)
         (with-current-buffer value-or-buffer
           (vc-run-delayed-success 1
             (funcall cb (diff-hl-changes-from-buffer (current-buffer)))))