[APX PPX] Avoid generating unmatched pushp/popp in pro/epilogue

According to APX spec, the pushp/popp pairs should be matched,
otherwise the PPX hint cannot take effect and cause performance loss.

In the ix86_expand_epilogue, there are several optimizations that may
cause the epilogue using mov to restore the regs. Check if PPX applied
and prevent usage of mov/leave in the epilogue. Also do not use PPX
for eh_return.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_expand_prologue): Set apx_ppx_used
	flag in m.fs with TARGET_APX_PPX && !crtl->calls_eh_return.
	(ix86_emit_save_regs): Emit ppx is available only when
	TARGET_APX_PPX && !crtl->calls_eh_return.
	(ix86_expand_epilogue): Don't restore reg using mov when
	apx_ppx_used flag is true.
	* config/i386/i386.h (struct machine_frame_state):
	Add apx_ppx_used flag.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/apx-ppx-2.c: New test.
	* gcc.target/i386/apx-ppx-3.c: Likewise.