This is really two changes in one but given interdependencies
and expected review latency I needed to combine the CLs.
1. Made the 5* toolpath build using the go build
system. Hooked the subdirectories to clean.bash but added a
separate make5.bash for now. Minor massage to make the code
more similar to the current structure of 6c/6a/6l.
2. Change all references from long to int32 in line with
similar change for the other toolchains.
The end result is that 5c, 5a and 5l can now be compiled and
the executables start up properly. Haven't thrown any input at
them yet.