Increment length by 1 if the relocation token is removed

gas/

	PR gas/15019
	* config/tc-i386.c (lex_got): Increment length by 1 if the
	relocation token is removed.

gas/testsuite/

	PR gas/15019
	* gas/i386/reloc32.s: Add tests for "xtrn@got -/+ 4".
	* gas/i386/reloc64.s: Likewise.
	* gas/i386/ilp32/reloc64.s: Likewise.

	* gas/i386/reloc32.d: Updated.
	* gas/i386/reloc64.d: Likewise.
	* gas/i386/ilp32/reloc64.d: Likewise.