[OpenCL] Fix diagnosing enqueue_kernel call with too few args

The err_typecheck_call_too_few_args diagnostic takes arguments, but
none were provided causing clang to crash when attempting to diagnose
an enqueue_kernel call with too few arguments.

Fixes llvm.org/PR42045

Differential Revision: https://reviews.llvm.org/D66883

llvm-svn: 370322