Define __CET__ for -fcf-protection and remove -mibt

Define __CET__ for -fcf-protection and remove -mibt

With revision 259496:

commit b1384095a7c1d06a44b70853372ebe037b2f7867
Author: hjl <hjl@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Thu Apr 19 15:15:04 2018 +0000

    x86: Enable -fcf-protection with multi-byte NOPs

-mibt does nothing and can be removed.  Define __CET__ to indicate level
protection with -fcf-protection:

(__CET__ & 1) != 0: -fcf-protection=branch or -fcf-protection=full
(__CET__ & 2) != 0: -fcf-protection=return or -fcf-protection=full

gcc/

	PR target/85469
	* common/config/i386/i386-common.c (OPTION_MASK_ISA_IBT_SET):
	Removed.
	(OPTION_MASK_ISA_IBT_UNSET): Likewise.
	(ix86_handle_option): Don't handle OPT_mibt.
	* config/i386/cet.h: Check __CET__ instead of __IBT__ and
	__SHSTK__.
	* config/i386/driver-i386.c (host_detect_local_cpu): Remove
	has_ibt and ibt.
	* config/i386/i386-c.c (ix86_target_macros_internal): Don't
	check OPTION_MASK_ISA_IBT nor flag_cf_protection.
	(ix86_target_macros): Define __CET__ with flag_cf_protection
	for -fcf-protection.
	* config/i386/i386.c (isa2_opts): Remove -mibt.
	* config/i386/i386.h (TARGET_IBT): Removed.
	(TARGET_IBT_P): Likewise.
	(ix86_valid_target_attribute_inner_p): Don't check OPT_mibt.
	* config/i386/i386.md (nop_endbr): Don't check TARGET_IBT.
	* config/i386/i386.opt (mcet): Update help message.
	(mshstk): Likewise.
	(mibt): Removed.
	* doc/invoke.texi: Remove -mibt.  Document __CET__.  Document
	-mcet as an alias for -mshstk.

gcc/testsuite/

	PR target/85469
	* gcc.target/i386/pr85044.c (dg-options): Remove -mibt.
	* gcc.target/i386/sse-26.c (dg-options): Remove -mno-ibt.

From-SVN: r259522