[llvm] [bazel] Add explicit dep on protobuf (PR #168928)

[Jordan Rupprecht via llvm-commits]

================
@@ -3,34 +3,35 @@
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 """bzlmod configuration for llvm-project"""
+
 module(name = "llvm-project-overlay")
 
 bazel_dep(name = "apple_support", version = "1.24.1", repo_name = "build_bazel_apple_support")
 bazel_dep(name = "bazel_skylib", version = "1.8.2")
 bazel_dep(name = "platforms", version = "1.0.0")
+bazel_dep(name = "protobuf", version = "31.1", repo_name = "com_google_protobuf")
----------------
rupprecht wrote:

At a glance, it does seem like we should be able to create clang/tools/clang-fuzzer/BUILD.bazel, and move proto_library + associated targets there. But, I recall this issue came up before, and yet the targets are still here... not sure if something prevented a move or we just didn't do it. Either way, I can take a look at doing that on Monday. Is that sufficient, or do you need changes in MODULE.bazel too?

As for the `bazel_dep` itself, the only way AFAIK to make something like this optional is to mark it as a dev dependency, which usually means deps only needed for running tests. A fuzzer is a bit more than a regular test, but probably not something that anyone is actually shipping in a toolchain, so maybe that's fine. @keith, would marking this `dev_dependency=True` be a good idea? Otherwise, I'm not sure what change we could make here.

Out of curiosity: what do you mean when you say it's large? Not doubting your claim, just trying to understand better. e.g. is it adding XX MiB to your build footprint or XX seconds/minutes to your build process?

https://github.com/llvm/llvm-project/pull/168928