Backport #909: rpath fix for garden

[scpeters]

🦟 Bug fix

Backport #909 to garden

Summary

Sets the ogre2 target INSTALL_RPATH to a copy of
CMAKE_INSTALL_RPATH with OGRE_LIBRARY_DIRS
appended, instead of just the latter path. This
helps with packaging on macOS.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Rebase-and-Merge

[codecov]

Codecov Report

Merging #912 (541faad) into gz-rendering7 (59417ba) will not change coverage.
The diff coverage is n/a.

❗ Current head 541faad differs from pull request most recent head 89b30a0. Consider uploading reports for the commit 89b30a0 to get more accurate results

@@              Coverage Diff               @@
##           gz-rendering7     #912   +/-   ##
==============================================
  Coverage          77.22%   77.22%           
==============================================
  Files                170      170           
  Lines              14721    14721           
==============================================
  Hits               11369    11369           
  Misses              3352     3352           

[scpeters]

windows failures seem to be described by #745 and look unrelated to this PR. I'll go ahead and merge