cmake-mode.el: Add font-lock for keywords and variables

Control flow keywords will now be highlighted as such.  Variable names
will be also be recognized.  Adjust function name highlighting to work
in places other than the start of a line.

Auxiliary/cmake-mode.el

@@ -193,9 +193,17 @@ the indentation.  Otherwise it retains the same position on the line"
 ;; Keyword highlighting regex-to-face map.
 ;;
 (defconst cmake-font-lock-keywords
-  (list '("^[ \t]*\\([[:word:]_]+\\)[ \t]*(" 1 font-lock-function-name-face))
-  "Highlighting expressions for CMAKE mode."
-  )
+  `((,(rx-to-string `(and symbol-start
+                          (or ,@cmake-keywords
+                              ,@(mapcar #'downcase cmake-keywords))
+                          symbol-end))
+     . font-lock-keyword-face)
+    (,(rx symbol-start (group (+ (or word (syntax symbol)))) ?\()
+     1 font-lock-function-name-face)
+    ("\\${?\\([[:alpha:]_][[:alnum:]_]*\\|[0-9]+\\|[$*_]\\)"
+     1 font-lock-variable-name-face t)
+    )
+  "Highlighting expressions for CMake mode.")
 
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