Fix build errors on Linux

As reported here: https://groups.google.com/d/topic/runtimecompiledcplusplus/0SMPjmI1524/discussion

The CMake build is missing the link to pthread on Linux. Looking at the documentation here: http://www.glfw.org/release-2.7.7.html#22_x11_on_unixlike_systems it says:

> _GLFW_HAS_PTHREAD	
> Use the POSIX Threads API for threading. This is the only supported API for the X11 port. Without it, threading will be disabled.

The static library provided Aurora/External/glfw/libX11/libglfw.a has been built with pthread support.

On Linux, `PTHREAD_MUTEX_INITIALIZER` can only be used at the ~definition of a variable (such as init list or whatever accept braces initialization).