x86: Add -mneeded for GNU_PROPERTY_X86_ISA_1_V[234] marker

x86: Add -mneeded for GNU_PROPERTY_X86_ISA_1_V[234] marker

GCC 11 supports -march=x86-64-v[234] to enable x86 micro-architecture ISA
levels:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97250

Binutils has been updated to support GNU_PROPERTY_X86_ISA_1_V[234] marker:

https://gitlab.com/x86-psABIs/x86-64-ABI/-/merge_requests/13

with

commit b0ab06937385e0ae25cebf1991787d64f439bf12
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Oct 30 06:49:57 2020 -0700

    x86: Support GNU_PROPERTY_X86_ISA_1_BASELINE marker

and

commit 32930e4edbc06bc6f10c435dbcc63131715df678
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Fri Oct 9 05:05:57 2020 -0700

    x86: Support GNU_PROPERTY_X86_ISA_1_V[234] marker

in x86 ELF binaries.

Add -mneeded to emit GNU_PROPERTY_X86_ISA_1_NEEDED property to indicate
the micro-architecture ISA level required to execute the binary.

gcc/

	* config.gcc: Replace cet.o with gnu-property.o.  Replace
	i386/t-cet with i386/t-gnu-property.
	* config/i386/cet.c: Renamed to ...
	* config/i386/gnu-property.c: This.
	(emit_gnu_property): New function.
	(file_end_indicate_exec_stack_and_cet): Renamed to ...
	(file_end_indicate_exec_stack_and_gnu_property): This.  Call
	emit_gnu_property to generate GNU_PROPERTY_X86_FEATURE_1_AND and
	GNU_PROPERTY_X86_ISA_1_NEEDED properties.
	* config/i386/i386.opt (mneeded): New.
	* config/i386/linux-common.h (file_end_indicate_exec_stack_and_cet):
	Renamed to ...
	(file_end_indicate_exec_stack_and_gnu_property): This.
	(TARGET_ASM_FILE_END): Updated.
	* config/i386/t-cet: Renamed to ...
	* config/i386/t-gnu-property: This.
	(cet.o): Renamed to ...
	(gnu-property.o): This.
	* doc/invoke.texi: Document -mneeded.

gcc/testsuite/

	* gcc.target/i386/x86-needed-1.c: New test.
	* gcc.target/i386/x86-needed-2.c: Likewise.
	* gcc.target/i386/x86-needed-3.c: Likewise.