CMake: Ensure strict compiler flags for core projects

Previously we would accidentally miss out some of the compile flags.
This fixes these mentions :)

Change-Id: Ia593a1b2ed3aaf57750fa1bc601a0da1c92f3280
Reviewed-on: http://review.couchbase.org/42772
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>