[Format] Add machine-readable SPDX license ID to clang-format.el

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374864 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/clang-format/clang-format.el b/tools/clang-format/clang-format.el
index 0b9dc8d..3096ec1 100644
--- a/tools/clang-format/clang-format.el
+++ b/tools/clang-format/clang-format.el
@@ -2,6 +2,7 @@
 
 ;; Keywords: tools, c
 ;; Package-Requires: ((cl-lib "0.3"))
+;; SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 ;;; Commentary: