[llvm] [libsycl] Move and rename the shared library (PR #188770)

[Sergey Semenov via llvm-commits]

sergey-semenov wrote:

@tahonermann It's the other way around, the change makes the install location of the library dependent on `LLVM_ENABLE_PER_TARGET_RUNTIME_DIR`, while removing that dependency for the build location.
So we go from "build/lib/x86_64-unknown-linux-gnu/libsycl.so" to "build/lib/libLLVMSYCL.so", and from "install/lib/libsycl.so" to "install/lib/x86_64-unknown-linux-gnu/libLLVMSYCL.so", which is how the other runtimes seem to handle it.

https://github.com/llvm/llvm-project/pull/188770