[committed] Add support for MIPS16e save/restore instructions

[David Ung]

I notice that mipsisa32r2-elfoabi dosen't yet build mips16 multilibs.
This patch is currently failing when building the dwarf unwind in libgcc.

David.

> gcc/
> 2007-07-02  Sandra Loosemore  <sandra@codesourcery.com>
> 	    Richard Sandiford  <richard@codesourcery.com>
> 	    Nigel Stephens  <nigel@mips.com>
> 
> 	* config/mips/mips-protos.h (mips16e_save_restore_info): New struct.
> 	(mips16e_output_save_restore): Declare.
> 	(mips16e_save_restore_pattern_p): Likewise.
> 	* config/mips/mips.h (GENERATE_MIPS16E_SAVE_RESTORE): New macro.
> 	* config/mips/mips.c (MIPS_MAX_FIRST_STACK_STEP): Return 0x7f8
> 	for GENERATE_MIPS16E_SAVE_RESTORE.  Return 0x400 for TARGET_MIPS16
> 	&& !GENERATE_MIPS16E_SAVE_RESTORE && !TARGET_64BIT.
> 	(BITSET_P): New global macro, extracted from...
> 	(mips_for_each_saved_reg): ...here.
> 	(mips16e_save_restore_info): New struct.
> 	(mips16e_s2_s8_regs, mips16e_a0_a3_regs): New variables.
> 	(mips16e_save_restore_regs): New variable.
> 	(mips_split_plus, mips16e_find_first_register): New functions.
> 	(mips16e_mask_registers): New function.
> 	(compute_frame_size): Expand the commentary before the function.
> 	Enforce the MIPS16e save and restore register range restrictions.
> 	Pad the general register save area at the low end.
> 	(mips16e_save_restore_reg, mips16e_build_save_restore)
> 	(mips16e_save_restore_pattern_p, mips16e_add_register_range)
> 	(mips16e_output_save_restore, mips16e_collect_propagate_value)
> 	(mips16e_collect_argument_save, mips16e_collect_argument_saves):
> 	New functions.
> 	(mips_expand_prologue, mips_expand_epilogue): Handle
> 	GENERATE_MIPS16E_SAVE_RESTORE.
> 	* config/mips/mips.md (*mips16e_save_restore): New pattern.