x86: Properly handle PLT expression in directive

x86: Properly handle PLT expression in directive

For PLT expressions, we should subtract the PLT relocation size only for
jump instructions.  Since PLT relocations are PC relative, we only allow
"symbol@PLT" in PLT expression.

gas/

	PR gas/23997
	* config/tc-i386.c (x86_cons): Check for invalid PLT expression.
	(md_apply_fix): Subtract the PLT relocation size only for jump
	instructions.
	* testsuite/gas/i386/reloc32.s: Add test for invalid PLT
	expression.
	* testsuite/gas/i386/reloc64.s: Likewise.
	* testsuite/gas/i386/ilp32/reloc64.s: Likewise.
	* testsuite/gas/i386/reloc32.l: Updated.
	* testsuite/gas/i386/reloc64.l: Likewise.
	* testsuite/gas/i386/ilp32/reloc64.l: Likewise.

ld/

	PR gas/23997
	* testsuite/ld-i386/i386.exp: Run PR gas/23997 test.
	* testsuite/ld-x86-64/x86-64.exp: Likewise.
	* testsuite/ld-x86-64/pr23997a.s: New file.
	* testsuite/ld-x86-64/pr23997b.c: Likewise.
	* testsuite/ld-x86-64/pr23997c.c: Likewise.