Add prototypes for all static functions and clean up some definitions.

(struct decompose): Move to before function declarations.
(secondary_memlocs_elim): One per operand, not per mode.
(get_secondary_mem): Accept and use reload description (opnum and type).
(push_reload): Accept and use new reload description instead of old NEEDED_FOR.
Define two new macros: MERGEABLE_RELOADS and MERGE_TO_OTHER.
Use these macros to see if reloads can be merged and how to do it.
(transfer_replacements): New function.
(combine_reloads): Refine when we can combine reloads.
(find_reloads): Use new method of tracking what a reload is for.
When we make a CLOBBER insn, do so with DImode.
Merge cases of making optional reloads, avoid making output-only optional
reloads, refine when we may not make in-out optional reloads, and make an
optional reload for a pair of matching operands.
(find_reloads_toplev, find_reloads_address{,_1, part}): Accept and use reload
description.
(forget_volatility): Delete long-obsolete function.

From-SVN: r3911