[Bug bootstrap/18033] --disable-aix64 doesn't remove ppc64 from multilib list

[askees at appfluent dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   GCC host triplet|                            |powerpc-ibm-aix5.1.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18033