Explicitly set OpenMP runtime library rpath like other normal libraries

[ye-luo]

Proposed changes

This should resolve OpenMP runtime library mismatch issue at runtime.

What type(s) of changes does this code introduce?

• Bugfix
• Build related changes

Does this introduce a breaking change?

• No

What systems has this change been tested on?

epyc-server

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• Yes. Code added or changed in the PR has been clang-formatted

[ye-luo]

Test this please

[prckent]

Can you explain how this helps someone running build/bin/qmcpack ? It does look like it will help for ctest runs.

We'll also have to carefully test on e.g. a good sampling of the different platforms we have build recipes for.

[ye-luo]

Test this please

[ye-luo]

BUILD_RPATH embeds rpath/runpath when linking executables in the build directory. When we run ctest, this info will be used for look up libraries although the priority is lower than environment variable LD_LIBRARY_PATH.
INSTALL_RPATH makes sure rpath/runpath are kept after make install

Once QMCPACK is built and/or installed. There is no longer a need to handle LD_LIBRARY_PATH for looking up OpenMP runtime libraries of any compiler at runtime.

[ye-luo]

Test this please

[PDoakORNL]

LGTM

[ye-luo]

Test this please