Matthew Pickering authored Jun 17, 2021 and Zubin committed Jun 25, 2021

The specification is now simple

* On linux, use `-Xlinker -rpath -Xlinker` to set the rpath of the
executable
* On darwin, never use `-Xlinker -rpath -Xlinker`, always inject
the rpath afterwards, see `runInjectRPaths`.
* If `-fno-use-rpaths` is passed then *never* inject anything into the
rpath.

Fixes #20004

(cherry picked from commit 6281a333)