[RA]: Fixing LRA cycling for multi-reg variable containing a fixed reg

[RA]: Fixing LRA cycling for multi-reg variable containing a fixed reg

PR111971 test case uses a multi-reg variable containing a fixed reg.  LRA
rejects such multi-reg because of this when matching the constraint for
an asm insn.  The rejection results in LRA cycling.  The patch fixes this issue.

gcc/ChangeLog:

	PR rtl-optimization/111971
	* lra-constraints.cc: (process_alt_operands): Don't check start
	hard regs for regs originated from register variables.

gcc/testsuite/ChangeLog:

	PR rtl-optimization/111971
	* gcc.target/powerpc/pr111971.c: New test.