Remove conflicting define
Fix CMake files to improve cross compiling

There was redundant information along with hard coded paths that did
not need to be present. This posed an issue for Windows users as the
hard coded paths were specific to Unix.
Add libtga library

Completely untested at the moment on the Sega Saturn, but it seems to
decode certain TARGA files just fine
Merge remote-tracking branch 'origin/CMake' into kernel