[CUDA] Make empty parameter lists in nvptx function decls easier to read.

Summary:
Before:

  .func  (.param .b32 func_retval0) _ZL21__nvvm_reflect_anchorv(

  )
  {

After:

  .func  (.param .b32 func_retval0) _ZL21__nvvm_reflect_anchorv()
  {

Reviewers: bkramer

Subscribers: llvm-commits, tra, jhen, echristo, jholewinski

Differential Revision: http://reviews.llvm.org/D16512

llvm-svn: 258637