Rename the opt plugin shared object to cuda_fixers.so

This is a more generic name, and I can link multiple passes into it.
Add implementation of the report-cuda-kernels pass.

This pass will read the nvvm.annotations metadata inserted into a module by
the frontend and report the name of the externally visible kernels in that
module.

This information can then be used by the compiler driver to run the internalize
pass appropriately.

The new pass is compiled into the cuda_fixers shared object, but not used in
the driver yet.