LU-16751 build: remove symlinks and add SPDX

LU-16751 build: remove symlinks and add SPDX

Remove commit-msg and prepare-commit-msg links
in the build/ directory. Add proper headers and
SPDX to the remaining files in build/.

Test-Parameters: trivial
Fixes: 25c93758d6 ("LU-1199 build: Clean out the build directory")
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I649ed60f5541be2832555efa2e0cf64cd1a5c67c
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53396
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>