Squash config.h and config_static.h

CMake isn't as bad as gnu autoconf when it comes to
regenerating files.

Change-Id: I00f215f698d0c950c923c0cb3a7df90d5e4bc50a
Reviewed-on: http://review.couchbase.org/34775
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>