[PR114810][LRA]: Recognize alternatives with lack of available registers for insn...

[PR114810][LRA]: Recognize alternatives with lack of available registers for insn and demote them.

  PR114810 was fixed in machine-dependent way.  This patch is a fix of
the PR on LRA side.  LRA chose alternative with constraints `&r,r,ro`
on i686 when all operands of DImode and there are only 6 available
general regs.  The patch recognizes such case and significantly
increase the alternative cost.  It does not reject alternative
completely.  So the fix is safe but it might not work for all
potentially possible cases of registers lack as register classes can
have any relations including subsets and intersections.

gcc/ChangeLog:

	PR target/114810
	* lra-constraints.cc (process_alt_operands): Calculate union reg
	class for the alternative, peak matched regs and required reload
	regs.  Recognize alternatives with lack of available registers and
	make them costly.  Add debug print about this case.