[llvm] [bazel] Add filegroup for builtin_headers (PR #67757)

[David Zbarsky via llvm-commits]

https://github.com/dzbarsky created https://github.com/llvm/llvm-project/pull/67757

I'd like to package these files into a distribution tar as part of https://github.com/dzbarsky/static-clang. I'm currently applying patches to the llvm repo but figured this bit could be upstreamed.

(Also open to ideas what to do about the `config.bzl` change in https://github.com/dzbarsky/static-clang/blob/master/llvm.patch - it's needed to link with musl libc)

>From fc691101c003b9ef22a772b72bf7c98c568238da Mon Sep 17 00:00:00 2001
From: David Zbarsky <dzbarsky at gmail.com>
Date: Thu, 28 Sep 2023 20:48:54 -0400
Subject: [PATCH] [bazel[ Add filegroup for builtin_headers

---
 utils/bazel/llvm-project-overlay/clang/BUILD.bazel | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/utils/bazel/llvm-project-overlay/clang/BUILD.bazel b/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
index cac8ec120929a37..4f7a5c7a47c68f4 100644
--- a/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/clang/BUILD.bazel
@@ -1693,6 +1693,11 @@ builtin_headers = glob(
     "lib/Headers/openmp_wrappers/new",
 ]
 
+filegroup(
+    name = "builtin_headers_files",
+    srcs = builtin_headers,
+)
+
 genrule(
     name = "builtin_headers_gen",
     srcs = builtin_headers,