(1) Modified X86 pass to now not do code gen if any visiting node has a genFunc

    set. This is important so as not to fail in case of 2-level PTX kernel,
    where the intermediate node does not have a gen function, but would pass
    because its parent has one.
(2) Modified PTX pass to
    i.  Correct mapping of arguments between intermediate and kernel launch node
    ii. Allow both constants and arguments as node limit values
    iii.Generate get_group_id and get_global_id correctly

M    Transforms/DFG2LLVM_X86/DFG2LLVM_X86.cpp
M    Transforms/DFG2LLVM_NVPTX/DFG2LLVM_NVPTX.cpp