kernel: Block HIP detection through HIP_PATH=none

The issue of the multi-lined, wrongly expanded LINUX_COMPILER macro is
back (at least for kernel 4.14).

Funnily enough, setting "--hip-path=/dev/null", or using any other file
or directory that exists, would still make clang happy and give a
message stating that it detected HIP anyways:

  Found HIP installation: /dev/null, version 3.5.0

To get around this issue, without doing monumental backports and
avoiding warnings from "-Wunused-command-line-argument", set
"HIP_PATH=none", where "none" simply indicates a non-existing
file/directory.

Change-Id: Ia97d69425716d28208ba344bde79a910e5f75c84
Signed-off-by: voidanix <voidanix@keyedlimepie.org>