libctf, binutils: fix big-endian libctf archive opening

libctf, binutils: fix big-endian libctf archive opening

The recent commit "libctf, binutils: support CTF archives like objdump"
broke opening of CTF archives on big-endian platforms.

This didn't affect anyone much before now because the linker never
emitted CTF archives because it wasn't detecting ambiguous types
properly: now it does, and this bug becomes obvious.

Fix trivial.

libctf/
	* ctf-archive.c (ctf_arc_bufopen): Endian-swap the archive magic
	number if needed.