Automerge: [gn] port 4e9e7c5

Author: nico

llvm/utils/gn/secondary/clang-tools-extra/clang-doc/tool/BUILD.gn

@@ -6,6 +6,7 @@ copy("assets") {
     "../assets/comment-template.mustache",
     "../assets/enum-template.mustache",
     "../assets/function-template.mustache",
+    "../assets/head-template.mustache",
     "../assets/index.js",
     "../assets/mustache-index.js",
     "../assets/namespace-template.mustache",