Dan Kegel authored Sep 09, 2016 and Brad King committed Sep 12, 2016

Since we support adding arbitrary flags to the link line via
`target_link_libraries` the project/user may add their own RPATH flags
(typically for system library locations).  Re-order the link line to
place our generated RPATH entries before the libraries so that they also
come before flag-specified entries.  Otherwise our in-build-tree RPATH
entries may not be preferred by the dynamic loader and we could collide
with libraries in the system directories.

Closes: #16293