ld: Pass -z separate-code to ld for property-x86-4a tests

ld: Pass -z separate-code to ld for property-x86-4a tests

Pass -z separate-code to ld for property-x86-4a tests to generate
the expected .note.gnu.property section.  Also run i386 tests for
x86_64-*-elf* targets.

	* testsuite/ld-i386/i386.exp: Also run for x86_64-*-elf* targets.
	* testsuite/ld-i386/property-x86-4a.d: Pass -z separate-code to
	ld.
	* testsuite/ld-x86-64/property-x86-4a-x32.d: Likewise.
	* testsuite/ld-x86-64/property-x86-4a.d: Likewise.