Fix missing library when linking GLFW3
Move the set line to be excluded from the Win32 section
Remove the static library preference instead of trying to link against
it.

To build Sigma, glfw3 must be built from source using the command:

cmake -DBUILD_SHARED_LIBS=ON
Merge pull request #76 from catageek/fix_glfw_build_errors

Fix missing library when linking GLFW3