mips64-linux.
* ld-elf/merge.d: Xfail on mips64*-linux-gnu*.
* ld-mips-elf/mips-elf-flags.exp (ldemul): Set to o32-compatible
on mips-sgi-irix6*, mips64-linux-gnu and mips64el-linux-gnu.
(good_combination, bad_combination): Use it.
Add -32 or -mabi=o64 wherever the ABI was formerly implied.