ira: Allow multiple uses within an insn [PR125173]

For the attached test we end up during IRA with

6: r99:DI=`s'
  REG_EQUIV `s'
7: {[`b']=asm_operands;
    [const(`s'+0x4)]=asm_operands;
    [`a']=asm_operands;clobber flags:CC;}
  REG_DEAD r99:DI
  REG_UNUSED flags:CC

where r99 is used in each asm_operands

(mem/c:SI (plus:DI (reg/f:DI 99)
                   (const_int 4 [0x4])) [2 s.d+0 S4 A32])

This in turn means that we hit multiple times the very same insn while
iterating over all uses of r99 which in the end triggers the assert.

This patch relaxes the assert since what we want to ensure here is that
a register is not used by multiple insns since otherwise we cannot
trivially move or delete the definition.

	PR rtl-optimization/125173

gcc/ChangeLog:

	* ira.cc (combine_and_move_insns): Allow multiple uses within
	an insn.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr125173-1.c: New test.

(cherry picked from commit 107d2ad166d09883b43ec1a5cf1e37c68b134a93)