When both GLFW_INCLUDE_VULKAN and VK_USE_PLATFORM_WIN32_KHR were
defined, the GLFW header would define replacement versions of APIENTRY
and WINGDIAPI /before/ including the Vulkan header, which would include
windows.h, which (justifiably) defines APIENTRY and WINGDIAPI blindly.

Fixes #1524.

(cherry picked from commit 773f4495f005004ea17fbc4a96b6b1ce758e79d6)