[Release] Produce mlir tarball

[nikic]

Summary

MLIR supports standalone builds, so I think it makes sense to also produce a release tarball for the MLIR subproject.

[thieta]

Makes sense to me. We probably should add bolt in there as well since it's enabled by default now, cc @Amir

[Amir]

In D141919#4058505, @thieta wrote:

Makes sense to me. We probably should add bolt in there as well since it's enabled by default now, cc @Amir

I'm not sure if BOLT supports a standalone build mode (we didn't add one). But I guess it's fine to create tarball with BOLT sources.

llvm/utils/release/export.sh

 #!/bin/bash
 #===-- tag.sh - Tag the LLVM release candidates ----------------------------===#
 #
 # Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 # See https://llvm.org/LICENSE.txt for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 #
 #===------------------------------------------------------------------------===#
 #
 # Create branches and release candidates for the LLVM release.
 #
 #===------------------------------------------------------------------------===#
 
 set -e
 
-projects="llvm clang cmake compiler-rt libcxx libcxxabi libclc clang-tools-extra polly lldb lld openmp libunwind flang third-party"
+projects="llvm clang cmake compiler-rt libcxx libcxxabi libclc clang-tools-extra polly lldb lld openmp libunwind mlir flang third-party"
 
 release=""
 rc=""
 yyyymmdd=$(date +'%Y%m%d')
 snapshot=""
 template='${PROJECT}-${RELEASE}${RC}.src.tar.xz'
 
 usage() {