Comment # 3 on bug 105200 from Jan Vesely

you'll need the libclc build fixes from:
http://lists.llvm.org/pipermail/libclc-dev/2018-February/002796.html
and
http://lists.llvm.org/pipermail/libclc-dev/2018-February/002800.html

(all 5 of them).
Alternatively you can wait until they land.