compat: Use org- wrapper for string-equal-ignore-case compatibility

* lisp/org-compat.el (org-string-equal-ignore-case): New compatibility
function.
(org-mode-flyspell-verify):
* lisp/ob-core.el (org-babel-results-keyword):
(org-babel-insert-result):
* lisp/org-lint.el (org-lint-duplicate-custom-id):
* lisp/ox.el (org-export-resolve-radio-link):
Use org-string-equal-ignore-case.

Prefer an explicit org- wrapper to isolate the kludge and avoid any
confusion about where it is defined.

This is a follow-up to the port of Emacs's 70341cab3.

lisp/ob-core.el

@@ -144,7 +144,7 @@ used."
   :type 'string
   :safe (lambda (v)
 	  (and (stringp v)
-	       (string-equal-ignore-case "RESULTS" v))))
+	       (org-string-equal-ignore-case "RESULTS" v))))
 
 (defcustom org-babel-noweb-wrap-start "<<"
   "String used to begin a noweb reference in a code block.
@@ -2491,7 +2491,7 @@ INFO may provide the values of these header arguments (in the
 		       ;; Escape contents from "export" wrap.  Wrap
 		       ;; inline results within an export snippet with
 		       ;; appropriate value.
-		       ((string-equal-ignore-case type "export")
+		       ((org-string-equal-ignore-case type "export")
 			(let ((backend (pcase split
 					 (`(,_) "none")
 					 (`(,_ ,b . ,_) b))))
@@ -2502,14 +2502,14 @@ INFO may provide the values of these header arguments (in the
 					   backend) "@@)}}}")))
 		       ;; Escape contents from "example" wrap.  Mark
 		       ;; inline results as verbatim.
-		       ((string-equal-ignore-case type "example")
+		       ((org-string-equal-ignore-case type "example")
 			(funcall wrap
 				 opening-line closing-line
 				 nil nil
 				 "{{{results(=" "=)}}}"))
 		       ;; Escape contents from "src" wrap.  Mark
 		       ;; inline results as inline source code.
-		       ((string-equal-ignore-case type "src")
+		       ((org-string-equal-ignore-case type "src")
 			(let ((inline-open
 			       (pcase split
 				 (`(,_)

lisp/org-compat.el

@@ -76,6 +76,9 @@
 (declare-function org-fold-show-all "org-fold" (&optional types))
 (declare-function org-fold-show-children "org-fold" (&optional level))
 (declare-function org-fold-show-entry "org-fold" (&optional hide-drawers))
+;; `org-string-equal-ignore-case' is in _this_ file but isn't at the
+;; top-level.
+(declare-function org-string-equal-ignore-case "org-compat" (string1 string2))
 
 (defvar calendar-mode-map)
 (defvar org-complex-heading-regexp)
@@ -116,9 +119,10 @@ the symbol of the calling function, for example."
       (when (not (equal attr cachedattr))
         (puthash sym attr org-file-has-changed-p--hash-table)))))
 
-(unless (fboundp 'string-equal-ignore-case)
+(if (fboundp 'string-equal-ignore-case)
+    (defalias 'org-string-equal-ignore-case #'string-equal-ignore-case)
   ;; From Emacs subr.el.
-  (defun string-equal-ignore-case (string1 string2)
+  (defun org-string-equal-ignore-case (string1 string2)
     "Like `string-equal', but case-insensitive.
 Upper-case and lower-case letters are treated as equal.
 Unibyte strings are converted to multibyte for comparison."
@@ -1358,7 +1362,7 @@ ELEMENT is the element at point."
 	  (and log
 	       (let ((drawer (org-element-lineage element '(drawer))))
 		 (and drawer
-		      (string-equal-ignore-case
+		      (org-string-equal-ignore-case
 		       log (org-element-property :drawer-name drawer))))))
 	nil)
        (t

lisp/org-lint.el

@@ -383,7 +383,7 @@ called with one argument, the key used for comparison."
    ast
    'node-property
    (lambda (property)
-     (and (string-equal-ignore-case
+     (and (org-string-equal-ignore-case
            "CUSTOM_ID" (org-element-property :key property))
 	  (org-element-property :value property)))
    (lambda (property _) (org-element-property :begin property))

lisp/ox.el

@@ -82,7 +82,6 @@
 (require 'org-element)
 (require 'org-macro)
 (require 'tabulated-list)
-(require 'subr-x)
 
 (declare-function org-src-coderef-format "org-src" (&optional element))
 (declare-function org-src-coderef-regexp "org-src" (fmt &optional label))
@@ -4457,7 +4456,7 @@ has type \"radio\"."
   (let ((path (org-string-clean-whitespace (org-element-property :path link))))
     (org-element-map (plist-get info :parse-tree) 'radio-target
       (lambda (radio)
-	(and (string-equal-ignore-case
+	(and (org-string-equal-ignore-case
 	      (org-string-clean-whitespace (org-element-property :value radio))
               path)
 	     radio))