alpha return address patch

[meissner@cygnus.com]

| > I don't think using RETURN_ADDR_RTX should force the return address into
| > the stack; the current code should be able to handle having the return
| > address in a register just fine.
| 
| Except that it is very difficult to handle writing to that value
| and having it be seen by the epilogue.
| 
| If you can suggest, perhaps, a way to do elimination such that
| one way we have a (mem (plus (reg FP) (const ofs))) and the
| other a (reg RA), I'd be delighted to use it.

Well there is always the hack I used in the rs6000 for the memory used to
convert between fp and ints.  I created a new fixed 'register' (at least the
rest of the compiler thinks it is a register) that really represents a storage
location (this is due to bad interactions between inlining and allocating
storage by hand).