[PATCH] Declare that musttail calls in variadic functions forward the ellipsis

[Nick Lewycky]

I haven't audited the codebase looking for places that assume that variadic callees must be passing in a discrete list of args, but every place I can think of (DAE, argpromotion, ipsccp) either skips varargs functions entirely or doesn't try to reason about the varargs part. Should be fine.

http://reviews.llvm.org/D4892