More compiler warning fixes

Created originally on Bitbucket by dmilligan (David Milligan)

Was already merged in Bitbucket before import, marked as merged by the import user

Source changeset not longer availableat the time of import. Commit listwill look empty

One I missed for the 1100D, fixes based on suggestions from Jarno Paananen, and fixed a new one. I'm assuming you don't want _malloc public so I didn't put it in the header, just put a prototype at the top of exmem, this probably isn't the best solution either.