rs6000: accurate num_insns_constant_gpr

rs6000: accurate num_insns_constant_gpr

Trunk gcc supports more constants to be built via two instructions:
e.g. "li/lis; xori/xoris/rldicl/rldicr/rldic".
And then num_insns_constant should also be updated.

Function "rs6000_emit_set_long_const" is used to build complicated
constants; and "num_insns_constant_gpr" is used to compute 'how
many instructions are needed" to build the constant. So, these
two functions should be aligned.

The idea of this patch is: to reuse "rs6000_emit_set_long_const" to
compute/record the instruction number(when computing the insn_num,
then do not emit instructions).

gcc/ChangeLog:

	* config/rs6000/rs6000.cc (rs6000_emit_set_long_const): Add new
	parameter to record number of instructions to build the constant.
	(num_insns_constant_gpr): Call rs6000_emit_set_long_const to compute
	num_insn.