[MIPS] If using branch likelies in MIPS sync code fill the delay slot

with a nop.

gcc/
	* config/mips/mips.c (mips_process_sync_loop): Place a 
	nop in the delay slot of the branch likely instruction.
	(mips_output_sync_loop): Ensure mips_branch_likely is 
	set before calling mips_output_sync_loop.
	(mips_sync_loop_insns): Likewise.

From-SVN: r217926