Fix bazel build --incompatible_no_implicit_file_export

[Benoit]

Summary

The Bazel build relies, for the two files enumerated in this diff, on the legacy implicit-export semantics described here:
https://bazel.build/reference/be/functions#exports_files

This documentation page encourages migrating away from this legacy behavior, and indeed we have a user who reported a Bazel build error and it appears that they were already using the new, stricter behavior:
https://github.com/openxla/iree/pull/13982
and while examining fixes on our side and trying to get a clean Bazel build, I ran into this similar issue in the LLVM overlay.

It would arguably be cleaner (in the sense of more structured) to rely on filegroup to export this, but I am insufficiently familiar with the Clang build (the dependent targets seem to be below Clang) to do this myself. The present exports_files solution has the merit of being localized in these few lines here.

[GMNGeoffrey]

Let's turn this flag on in the CI @aeubanks. We could maybe just put it in the bazelrc?

[aeubanks]

yeah in the bazelrc is good (not sure if these incompatible flags are present in all supported bazel versions though?)

[GMNGeoffrey]

In D152491#4419315, @aeubanks wrote:

yeah in the bazelrc is good (not sure if these incompatible flags are present in all supported bazel versions though?)

The flag was added in https://github.com/bazelbuild/bazel/commit/2bb1bf9422ba22d0e1ab15363664339f022b29a1, which was in Bazel 1.2. We definitely don't support things older than that (I'd guess we probably don't even support Bazel 4 or even 5 at this point given https://github.com/llvm/llvm-project/blob/main/utils/bazel/.bazelversion has 6.1)

[GMNGeoffrey]

@Benoit could you add the flag here? https://github.com/llvm/llvm-project/blob/main/utils/bazel/.bazelrc#L11

[Benoit]

Add the flag to .bazelrc

[aeubanks]

I'd land the two changes separately but both lgtm

[Benoit]

rebased

[aeubanks]

utils/bazel/.bazelrc

28

Opt

[Benoit]

Add more files discovered by running the CI Bazel command.

[Benoit]

more exported files. fix typo in comment.

utils/bazel/.bazelrc

 
 # Rely on compiler flags to compile with debug info/strip rather than stripping
 # based on compilation_mode.
 build --strip=never
 
 # Add layering check to all projects.
 build --features=layering_check
 
+# Out out of legacy lax behavior implicitly exporting files that are rule inputs
+# with default visibility.
+# See: https://bazel.build/reference/be/functions#exports_files
+build --incompatible_no_implicit_file_export
+
 ###############################################################################
 # Options to select different strategies for linking potential dependent
 # libraries. The default leaves it disabled.
 ###############################################################################
 
 build:zlib_external --repo_env=BAZEL_LLVM_ZLIB_STRATEGY=external
 build:zlib_system --repo_env=BAZEL_LLVM_ZLIB_STRATEGY=system
 

utils/bazel/llvm-project-overlay/llvm/BUILD.bazel

 
 package(
     default_visibility = ["//visibility:public"],
     features = ["layering_check"],
 )
 
 licenses(["notice"])
 
-exports_files(["LICENSE.TXT"])
+exports_files([
+    "LICENSE.TXT",
+    "cmake/modules/llvm-driver-template.cpp.in",
+    "include/llvm/Option/OptParser.td"
+])
 
 # It may be tempting to add compiler flags here, but that should be avoided.
 # The necessary warnings and other compile flags should be provided by the
 # toolchain or the `.bazelrc` file. This is just a workaround until we have a
 # widely available feature to enable unlimited stack frame instead of using
 # this `Make` variable.
 llvm_copts = [
     "$(STACK_FRAME_UNLIMITED)",