portage: the midipix porting bits for everything but the compiler

porting applications and libraries to midipix can often be done with no changes to the code proper, and only minor changes to the build system, most notably with respect to libtool.

for the sake of convenience and simplicity, each supported version of an upstream source tree has a patch named package-x.y.z.midipix.patch.

for packages not using libtool, building for the midipix target should only require the above patch file. if the package does use libtool, however, then you should also copy libtool.midipix to the top directory of its source tree.