Fix DW_CFA_GNU_args_size handling. The primary architecture using this
opcode is VAX. A function call pushes the number of arguments given onto
the stack and "ret" will pop it automatically. The FDE of the caller
contains the amount of stack space used for arguments (and possibly
extra padding), so unwinding has to compensate for this when "returning"
from a function. This is exactly the case when step() is done. The
existing handling in unw_set_reg no longer makes sense.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@204290 91177308-0d34-0410-b5e6-96231b3b80d8
Simplify.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@204292 91177308-0d34-0410-b5e6-96231b3b80d8