[LRA] Do not use eliminable registers for spilling

[LRA] Do not use eliminable registers for spilling

The liveness of eliminable hard registers is not tracked by LRA between
basic blocks, so they should not be used as spill registers as LRA may
decide to allocate them to pseudos while the spilled value is still live.

2019-11-10  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* lra-spills.c (assign_spill_hard_regs): Do not spill into
	registers in eliminable_regset.

From-SVN: r278024