Remove the 'build' directory by default

[comps]

Most OSS projects that use cmake let the user or a script create
the directory instead of it being pre-created.

While it might seems just like a convenience here, if you actually
remove the directory (to make a new build) and later commit with
git commit -a, the removal of build/.gitkeep will be added to
the commit.

.gitignore does not help here as it only prevents untracked files
from being added - changes in existing tracked files are still
registered.

While there are other local-only workarounds like

git update-index --skip-worktree build/.gitkeep

a cleaner solution is removing the default build dir altogether.

[scrutinizer-notifier]

The inspection completed: 2 new issues

[redhatrises]

Kind Nack. This is provided for content authors and not developers who are familiar with Cmake.

[comps]

The main problem I wanted to address was the removed .gitkeep getting in the way of git add -a rather than cmake ecosystem conformance. If you don't have problems with it polluting pull requests, feel free to close this PR - the change was really meant to help with project maintenance and if it doesn't help, it's useless.

I can re-submit the build_project multi-job tweak separately.

[redhatrises]

I can re-submit the build_project multi-job tweak separately.

@comps please do submit the build_project multi-job tweak separately.