Pass aggregates on the stack without splitting in NVPTX.

Following the NVVM IR specifications, arguments of aggregate type should be
passed on the stack without splitting (byval).

http://reviews.llvm.org/D6020

Patch by Jacques Pienaar.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220854 91177308-0d34-0410-b5e6-96231b3b80d8