ira: Fix unnecessary register spill

ira: Fix unnecessary register spill

The variables first_moveable_pseudo and last_moveable_pseudo aren't
reset after compiling a function, which means they leak into the first
scheduler pass of the following function. In some cases, this can cause
an extra spill during register allocation of the second function.

gcc/ChangeLog:

	* ira.c (move_unallocated_pseudos): Zero first_moveable_pseudo and
	last_moveable_pseudo before returning.

gcc/testsuite/ChangeLog:

	* gcc.target/aarch64/nospill.c: New test.