Updated to latest GLFW library and working on Wayland support, still
looking how to implement it on raylib because it just exposes
PLATFORM_DESKTOP and defaults to X11 windowing system on Linux...

OpenAL Soft backend is still available in audio module, I'm thinking if
exposing it for building in some way or just left it there for advance
users to switch to it manually in case of necessity...

There have been two problems:

* GLFW itself was compiled with the definitions for compiling
_against_ GLFW (fixed by removing requirement for external glfw)

* rglfw.c was being compiled as C code, although it includes
Objective C files.

This _might_ break the Windows build, needs to be checked.

Fixes #391, but as noted I'd prefer though a separate source directory
and build script for GLFW.

...to define proper values

Compiling GLFW library with raylib avoids external dependencies, this
way we solve version problems in some platforms