i386: Move struct ix86_frame to machine_function

i386: Move struct ix86_frame to machine_function

Make ix86_frame available to i386 code generation.  This is needed to
backport the patch set of -mindirect-branch= to mitigate variant #2 of
the speculative execution vulnerabilities on x86 processors identified
by CVE-2017-5715, aka Spectre.

	Backport from mainline
	2017-10-13  H.J. Lu  <hongjiu.lu@intel.com>

	PR target/82499
	* config/i386/i386.h (ix86_red_zone_size): New.

	2017-06-01  Bernd Edlinger  <bernd.edlinger@hotmail.de>

	* config/i386/i386.c (ix86_frame): Moved to ...
	* config/i386/i386.h (ix86_frame): Here.
	(machine_function): Add frame.
	* config/i386/i386.c (ix86_compute_frame_layout): Repace the
	frame argument with &cfun->machine->frame.
	(ix86_can_use_return_insn_p): Don't pass &frame to
	ix86_compute_frame_layout.  Copy frame from cfun->machine->frame.
	(ix86_can_eliminate): Likewise.
	(ix86_expand_prologue): Likewise.
	(ix86_expand_epilogue): Likewise.
	(ix86_expand_split_stack_prologue): Likewise.

From-SVN: r259408