[emacs] Highlight hexadecimal integer constants

Today I learnt about their existence (D158288), they just need to be prefixed
with a u or s.

Reviewed By: goldstein.w.n

Differential Revision: https://reviews.llvm.org/D158290

Author: lukel97

llvm/utils/emacs/llvm-mode.el

@@ -43,7 +43,7 @@
    ;; Floating point constants
    '("\\b[-+]?[0-9]+.[0-9]*\\([eE][-+]?[0-9]+\\)?\\b" . font-lock-preprocessor-face)
    ;; Hex constants
-   '("\\b0x[0-9A-Fa-f]+\\b" . font-lock-preprocessor-face)
+   '("\\b[us]?0x[0-9A-Fa-f]+\\b" . font-lock-preprocessor-face)
    ;; Keywords
    `(,(regexp-opt
        '(;; Toplevel entities