[PATCH] [NVPTX] Do not emit .weak symbols for NVPTX

[Justin Holewinski]

This looks fine for now, considering the same approach is taken for the .globl directive.  That said, we really need a better way to handle this.  Ptxas supports just enough GNU-style syntax to let us get by without a custom AsmStreamer in most cases, but not enough to avoid these annoying issues.

http://reviews.llvm.org/D6455