In cross builds looks at host system for default library path

[rossburton]

default_libdir() looks at the host paths to determine the default value of libdir:

• if /etc/debian_version exists
• if /usr/lib/lib64 exists

For native builds this is acceptable, but in cross builds these paths have no relevance. I believe these checks should be done only if the build isn't being cross-compiled.

[QuLogic]

Seems a dupe of #2535.

[rossburton]

Yes, thanks.