gn build: make clangd depend on clang resource headers

Summary:
clangd needs them to function properly, even though they are not
strictly required for the build.

Reviewers: thakis

Reviewed By: thakis

Subscribers: MaskRay, jkorous, arphaman, llvm-commits, kadircet

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62480

llvm-svn: 361828

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

@@ -11,6 +11,7 @@ executable("clangd") {
     "//clang/lib/Basic",
     "//clang/lib/Format",
     "//clang/lib/Frontend",
+    "//clang/lib/Headers",
     "//clang/lib/Sema",
     "//clang/lib/Tooling",
     "//clang/lib/Tooling/Core",