OSX host compiler doesn't like section headers so undef them in cr2hdr.c. Also fix a warning about empty if statement.

Created originally on Bitbucket by jpaana (Jarno Paananen)

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

Just a small fix to get cr2hdr compiling with Clang under OSX and a warning fix about empty if statement.