Keep .s files so that compiler output can be easily verified.
Removed apparently unneeded PRECIOUS statement (OSX).

Output files were being left in the working directory.

Build needs to be tested on cygwin, if it fails find a different
solution or revert this commit.
Deleting compiler output file that should not have been committed.
Fixing barometer related warnings when compiling without barometer
support.
Work-in-progress