Build the core library as a static library on OS X
Reverse a condition to simplify handling more platforms

This is simpler than having to list all unix platforms separately.
Don't build the cli tool as an app bundle on OS X

Command line tools are normal unix binaries on OS X, while full
GUI apps use the app bundle structure.
Don't pass --warnings=none to bison

This fixes building on OS X - the bison variant there doesn't support
that option.
Add a PLATFORM_APPLE define, use this where necessary

This still doesn't include proper packaging of the scripts into
the app bundle though, but is enough for running the app from
within the source tree.
Merge pull request #8 from mstorsjo/build-osx

Fix building and running on OS X