LU-17522 build: Distribute clang build infrastructure

LU-17522 build: Distribute clang build infrastructure

Macro files:
    lustre-toolchain.m4 lustre-compiler-plugins.m4
and directory:
   cc-plugins

Should be included in distributed files, unconditionally.

Lustre-change: https://review.whamcloud.com/53991
Lustre-commit: 881cc6384a5e37f0e64b56c1b34563b87dcc210d

Test-Parameters: trivial
Fixes: d684885098 ("LU-16961 clang: plugins and build system integration")
Signed-off-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Change-Id: I6ddedd82c6180ffd1c4134fda6af6df6bd23dd34
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/54351
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>