Users often call getArgumentList().size(), which is a linear way to get
the number of function arguments. arg_size(), on the other hand, is
constant time.
In general, the fact that arguments are stored in an iplist is an
implementation detail, so I've removed it from the Function interface
and moved all other users to the argument container APIs (arg_begin(),
arg_end(), args(), arg_size()).
Reviewed By: chandlerc
Differential Revision: https://reviews.llvm.org/D31052
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298010 91177308-0d34-0410-b5e6-96231b3b80d8