app/internal/window: work around missing MESA_EGL_NO_X11_HEADERS support

Some versions of eglplatform.h don't support the MESA_EGL_NO_X11_HEADER
define for cross-platform definitions of the EGL types. Remove the
define and use an explicit cast instead.

Fixes gio#46

Signed-off-by: Elias Naur <mail@eliasnaur.com>

app/internal/window/egl_linux.go

@@ -4,7 +4,6 @@ package window
 
 /*
 #cgo LDFLAGS: -lEGL
-#cgo CFLAGS: -DMESA_EGL_NO_X11_HEADERS
 
 #include <EGL/egl.h>
 #include <EGL/eglext.h>

app/internal/window/egl_wayland.go

@@ -38,7 +38,7 @@ func (w *window) eglDestroy() {
 }
 
 func (w *window) eglDisplay() _EGLNativeDisplayType {
-	return _EGLNativeDisplayType(w.display())
+	return _EGLNativeDisplayType(unsafe.Pointer(w.display()))
 }
 
 func (w *window) eglWindow(visID int) (_EGLNativeWindowType, int, int, error) {