RA: Constrain class of pic offset table pseudo to general regs

On some targets an integer pseudo can be assigned to a FP reg.  For
pic offset table pseudo it means we will reload the pseudo in this
case and, as a consequence, memory containing the pseudo might be
recognized as wrong one.  The patch fix this problem.

        PR target/109541

gcc/ChangeLog:

	* ira-costs.cc: (find_costs_and_classes): Constrain classes of pic
	offset table pseudo to a general reg subset.

gcc/testsuite/ChangeLog:

	* gcc.target/sparc/pr109541.c: New.