[OpenMP] Pass -v to PTXAS if it was passed to the driver.

Summary: When compiling code being offloaded by OpenMP to an NVIDIA GPU, pass the -v to PTXAS if it was passed to the CLANG driver.

Reviewers: arpith-jacob, caomhin, carlo.bertolli, ABataev, jlebar, hfinkel, tstellar

Reviewed By: jlebar

Subscribers: Hahnfeld, rengolin, cfe-commits

Differential Revision: https://reviews.llvm.org/D29644

llvm-svn: 310295