[OpenMP] Don't set device runtime debugging flags if using '-nogpulib'

We use globals to configure debugging at compile-time for the device
runtime. Because these are only used by the OpenMP runtime we shouldn't
define them if we aren't using the device runtime. When a user passes in
'-nogpulib' this indicates that we are not using the device runtime, so
we should check for the precense of this flag and not emit these globals
if used.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D125314