Make MaxScale build on more environments (e.g. OSX)

This is a personal observation.

While attempting to build MaxScale on my Mac I notice that it won't build because OSX does not have the expected [Linux] libaio library.

[myuser@myhost ~/github.com/mariadb-corporation/MaxScale/build]$ cmake ..
– CMake version: 3.2.3
CMake Error at cmake/macros.cmake:97 (message):
Could not find libaio <<====================================
Call Stack (most recent call first):
CMakeLists.txt:32 (check_deps)

– Configuring incomplete, errors occurred!
See also "/Users/myuser/github.com/mariadb-corporation/MaxScale/build/CMakeFiles/CMakeOutput.log".
See also "/Users/myuser/github.com/mariadb-corporation/MaxScale/build/CMakeFiles/CMakeError.log".
[myuser@myhost ~/github.com/mariadb-corporation/MaxScale/build]$
[myuser@myhost ~/github.com/mariadb-corporation/MaxScale/build]$ uname -a # OSX 10.10.4
Darwin mad8 14.4.0 Darwin Kernel Version 14.4.0: Thu May 28 11:35:04 PDT 2015; root:xnu-2782.30.5~1/RELEASE_X86_64 x86_64

Due to this currently MaxScale won't build. This limits my ability to test etc.

Perhaps the effort needed to support other operating systems like OSX or other UNIX varieties (FreeBSD etc) is not worthwhile, but many applications wrap some of these routines away from the rest of the code so that a broader set of operating systems can run the software. MariaDB and MySQL works on several platforms and do not have these limitations, though they do use libaio on Linux, so I assume that something similar could be done for MaxScale.

I guess this depends mainly on time and interest, but it would be nice to see this work on platforms such as OSX which are often used by developers or DBAs.

For now I can work around this using a local virtual machine and that is what I'll do.