GBE: fix clang's "incorrect" optimization for barrier call.

GBE: fix clang's "incorrect" optimization for barrier call.

Clang may duplicate one barrier call to multiple branches which
breaks opencl's spec and may cause gpu hang. To fix this issue,
we have to implement the barrier in a llvm module file and specify
the function attribute to noduplicate, and we have to link this
pre-compiled module before we compile the user kernel, so we set
it the pcm lib file to the LinkBitCodeFile field of the clang
instance.

v2: fix one typo.

Signed-off-by: Zhigang Gong <zhigang.gong@intel.com>
Reviewed-by: "Yang, Rong R" <rong.r.yang@intel.com>