Update cmake paths be relative to hiop project

[chapman39]

This PR will allow lido and other projects to utilize hiop as a submodule.

• Update cmake variables to use switch to using PROJECT_BINARY_DIR and PROJECT_SOURCE_DIR rather than their cmake counterparts. This should not affect regular hiop builds.

[chapman39]

Seems like I'm missing some permissions

https://github.com/LLNL/hiop/actions/runs/8270156566/job/22627066587?pr=684

remote: HTTP Basic: Access denied.
The provided password or token is incorrect or your account has 2FA enabled and you must use a personal access token instead of a password.
See https://gitlab.pnnl.gov/help/topics/git/troubleshooting_git#error-on-git-fetch-http-basic-access-denied

[cameronrutherford]

Reasonable changes, although I would recommend spack over submodules where appropriate

[cameronrutherford]

Seems like I'm missing some permissions

https://github.com/LLNL/hiop/actions/runs/8270156566/job/22627066587?pr=684

remote: HTTP Basic: Access denied.
The provided password or token is incorrect or your account has 2FA enabled and you must use a personal access token instead of a password.
See https://gitlab.pnnl.gov/help/topics/git/troubleshooting_git#error-on-git-fetch-http-basic-access-denied

PNNL CI error here isn't because of anything you have done. This is fine to merge IMO

[chapman39]

I do not have permission to merge this PR, but it is finished.