[Driver][SYCL] Restore libsycl.so detection on Linux/Unix (#22173)
Upstream commit ab31a3d590eb replaced the Linux/Unix library names with
libLLVMSYCL.so as a side effect.
In intel/llvm sycl branch we need to use libsycl.so, libLLVMSYCL.so does
not exist.
This is causing mutliple sycl test failures in sycl-web branch.
