CMake: Remove some extraneous definitions for autotools

This removes some definitions from the compiler line which shouldn't
really be needed for building with CMake

Change-Id: Ic358ce1c48e89010ffe14292f16c3e64cf11a597
Reviewed-on: http://review.couchbase.org/43717
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>