3 changes, 2 of which are cleanup one of which changes codegen:

1. Rearrange code a bit so that the special case doesn't require indenting lots
   of code.
2. Add comments describing PPC calling convention.
3. Only round up to 56-bytes of stack space for an outgoing call if the callee
   is varargs.  This saves a bit of stack space.

llvm-svn: 28342