[SYCL][sycl-xocc] Cleanup intermediate files sycl-xocc generates and places in /tmp/

[agozillon]

Not the biggest problem and rather useful for debugging right now, but we shouldn't really be filling a users /tmp/ directory with garbage files and not cleaning them up!

This could be linked into https://github.com/triSYCL/sycl/issues/25 so that when a user passes --save-temps to Clang, we do not clean up our intermediate files. However, there was a bug with using --save-temps when compiling for Intel devices and there is an open Issue on the Intel/SYCL repository relating to this it. Although, it appears that when altering the driver to use our own ToolChain and fpga/xilinx triple it may have inadvertently bypassed it