gas output_file_close error message

Seen on arm-elf, where ELFOSABI_ARM is set too late to get a warning
when processing ifunc related directives on their source line.
../gas/as-new ifunc.s -o tmpdir/ifunc.o
../gas/as-new: symbol type STT_GNU_IFUNC is supported only by GNU and FreeBSD targets
ifunc.s: Assembler messages:
ifunc.s: Fatal error: can't close tmpdir/ifunc.o: sorry, cannot handle this file

This patch doesn't fix the real underlying problem, just the late
error message where "can't close" is a misdirection in this case.

	* output-file.c (output_file_close): Remove "can't close" from
	error message.
	* testsuite/gas/mips/reginfo-2.l: Update expected output.