[SYCL] search the plugins at a path relative to the SYCL Runtime

[ph0b]

Client applications shipping on Linux need to be able to load sycl.dll and plugins without having to get user to tune LD_LIBRARY_PATH.
Per:

llvm/sycl/doc/design/PluginInterface.md

Line 51 in f6420c7

installation directory by using DT_RPATH on Linux. Similar functionality can be

Would it be possible to add at least $ORIGIN/../lib to libsycl RUNPATH?

[steffenlarsen]

Hi @ph0b! #6658 changed the search path of plugins to be relative to the SYCL runtime library. That does not let you control the path of the SYCL runtime library sadly. #6306 attempts to add some control for this, but there are some security concerns.

[ph0b]

Hey, I'm fine with #6658 solution for now, it does solve the reported issue.