Files built for Win32 must use C89 style declarations for compatibility
with VS 2010 and 2012, which are still supported by GLFW.
(cherry picked from commit 56aad76b16)
This adds glfwGetWindowContentScale and glfwGetMonitorContentScale for
querying the recommended drawing scale factor for DPI-aware rendering.
Parts of this patch are based on code by @ferreiradaselva.
Fixes#235.
Fixes#439.
Fixes#677.
Fixes#845.
Fixes#898.