Log Message:
As far as PowerPC support goes, libvpx supports 64-bit PowerPC in Little Endian
mode only, now. Set the target to generic-gnu for powerpc based ports on NetBSD
to allow libvpx to build and run, though without any targetted optimization.
Resolves build issue on NetBSD/macppc which failed at configure stage otherwise.

TenFourFox has patches to add support for Altivec acceleration, which could be
used to add support back again locally.
https://github.com/classilla/tenfourfox/tree/master/media/libvpx