[llvm] [emacs] More consistently highlight value keywords that appear in vectors (PR #97594)

[via llvm-commits]

================
@@ -61,6 +61,8 @@
    `(,(concat "\\<" llvm-mode-primitive-type-regexp "\\>") . font-lock-type-face)
    ;; Integer literals
    '("\\b[-]?[0-9]+\\b" . font-lock-preprocessor-face)
+   ;; Values that can appear in a vec
+   '("\\b\\(true\\|false\\|null\\|undef\\|poison\\|none\\)\\b" . font-lock-keyword-face)
----------------
goldsteinn wrote:

Full code:
```
'((concat "\\b\\(" (mapconcat 'identity '("true" "false" "null" "undef" "none" "poison") "\\|") "\\)\\b") . font-lock-keyword-face)
```

https://github.com/llvm/llvm-project/pull/97594