Backport commit 70341cab3 from Emacs

* lisp/ob-core.el (org-babel-results-keyword):
  Use `string-equal-ignore-case' instead of explicit `compare-strings'.
(org-babel-insert-result): Likewise.
* lisp/org-compat.el (string-equal-ignore-case):
  Define unless defined already.
(org-mode-flyspell-verify): Use `string-equal-ignore-case'.
* lisp/org-lint.el (org-lint-duplicate-custom-id): Likewise.
* lisp/ox.el (org-export-resolve-radio-link): Use
  `string-equal-ignore-case' and `string-clean-whitespace'.

string-equal-ignore-case: new function
70341cab3eb26e2f49bbc13d6bca247ab9403abc
Sam Steingold
Tue Jul 26 13:49:28 2022 -0400

[ km: Note that string-clean-whitespace also requires a compatibility
  kludge and the string-equal-ignore-case kludge was added to the
  wrong org-compat section.  These will be addressed in a follow-up
  commit. ]

lisp/ob-core.el

@@ -136,8 +136,7 @@ used."
   :type 'string
   :safe (lambda (v)
 	  (and (stringp v)
-	       (eq (compare-strings "RESULTS" nil nil v nil nil t)
-		   t))))
+	       (string-equal-ignore-case "RESULTS" v))))
 
 (defcustom org-babel-noweb-wrap-start "<<"
   "String used to begin a noweb reference in a code block.
@@ -2435,7 +2434,7 @@ 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.
-		       ((eq t (compare-strings type nil nil "export" nil nil t))
+		       ((string-equal-ignore-case type "export")
 			(let ((backend (pcase split
 					 (`(,_) "none")
 					 (`(,_ ,b . ,_) b))))
@@ -2446,14 +2445,14 @@ INFO may provide the values of these header arguments (in the
 					   backend) "@@)}}}")))
 		       ;; Escape contents from "example" wrap.  Mark
 		       ;; inline results as verbatim.
-		       ((eq t (compare-strings type nil nil "example" nil nil t))
+		       ((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.
-		       ((eq t (compare-strings type nil nil "src" nil nil t))
+		       ((string-equal-ignore-case type "src")
 			(let ((inline-open
 			       (pcase split
 				 (`(,_)

lisp/org-compat.el

@@ -934,6 +934,14 @@ Implements `define-error' for older emacsen."
     (put name 'error-conditions
          (copy-sequence (cons name (get 'error 'error-conditions))))))
 
+(unless (fboundp 'string-equal-ignore-case)
+  ;; From Emacs subr.el.
+  (defun 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."
+    (eq t (compare-strings string1 0 nil string2 0 nil t))))
+
 (unless (fboundp 'string-suffix-p)
   ;; From Emacs subr.el.
   (defun string-suffix-p (suffix string  &optional ignore-case)
@@ -1125,10 +1133,8 @@ ELEMENT is the element at point."
 	  (and log
 	       (let ((drawer (org-element-lineage element '(drawer))))
 		 (and drawer
-		      (eq (compare-strings
-			   log nil nil
-			   (org-element-property :drawer-name drawer) nil nil t)
-			  t)))))
+		      (string-equal-ignore-case
+		       log (org-element-property :drawer-name drawer))))))
 	nil)
        (t
 	(cl-case (org-element-type element)

lisp/org-lint.el

@@ -334,10 +334,8 @@ called with one argument, the key used for comparison."
    ast
    'node-property
    (lambda (property)
-     (and (eq (compare-strings "CUSTOM_ID" nil nil
-			       (org-element-property :key property) nil nil
-			       t)
-	      t)
+     (and (string-equal-ignore-case
+           "CUSTOM_ID" (org-element-property :key property))
 	  (org-element-property :value property)))
    (lambda (property _) (org-element-property :begin property))
    (lambda (key) (format "Duplicate CUSTOM_ID property \"%s\"" key))))

lisp/ox.el

@@ -80,6 +80,7 @@
 (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))
@@ -4436,15 +4437,12 @@ INFO is a plist used as a communication channel.
 
 Return value can be a radio-target object or nil.  Assume LINK
 has type \"radio\"."
-  (let ((path (replace-regexp-in-string
-	       "[ \r\t\n]+" " " (org-element-property :path link))))
+  (let ((path (string-clean-whitespace (org-element-property :path link))))
     (org-element-map (plist-get info :parse-tree) 'radio-target
       (lambda (radio)
-	(and (eq (compare-strings
-		  (replace-regexp-in-string
-		   "[ \r\t\n]+" " " (org-element-property :value radio))
-		  nil nil path nil nil t)
-		 t)
+	(and (string-equal-ignore-case
+	      (string-clean-whitespace (org-element-property :value radio))
+              path)
 	     radio))
       info 'first-match)))