[OpenCL] Enabling the usage of CLK_NULL_QUEUE as compare operand.

Summary: Enabling the compression of CLK_NULL_QUEUE to variable of type queue_t.

Reviewers: Anastasia

Subscribers: cfe-commits, yaxunl, bader

Differential Revision: https://reviews.llvm.org/D27569

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@290171 91177308-0d34-0410-b5e6-96231b3b80d8