Add x86_64-unknown-linux. Personally I think amd64 is a better name
than x86_64, but it looks like that's what the GNU folks have gone for.
HostVendor_CPP='unknown'
HostOS_CPP='linux'
;;
+x86_64-*-linux*)
+ HostPlatform=x86_64-unknown-linux
+ TargetPlatform=x86_64-unknown-linux
+ BuildPlatform=x86_64-unknown-linux
+ HostPlatform_CPP='x86_64_unknown_linux'
+ HostArch_CPP='x86_64'
+ HostVendor_CPP='unknown'
+ HostOS_CPP='linux'
+ ;;
m68k-next-nextstep2)
HostPlatform_CPP='m68k_next_nextstep2'
HostArch_CPP='m68k'