internal/egl: replace glFinish with eglWaitClient

glFinish depends on package gl which is about to require a function
pointer loader. eglWaitClient is in the EGL API and always available.

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

internal/egl/egl_windows.go

@@ -40,6 +40,7 @@ var (
 	_eglSwapBuffers         = libEGL.NewProc("eglSwapBuffers")
 	_eglTerminate           = libEGL.NewProc("eglTerminate")
 	_eglQueryString         = libEGL.NewProc("eglQueryString")
+	_eglWaitClient          = libEGL.NewProc("eglWaitClient")
 )
 
 var loadOnce sync.Once
@@ -156,6 +157,11 @@ func eglQueryString(disp _EGLDisplay, name _EGLint) string {
 	return syscall.BytePtrToString((*byte)(unsafe.Pointer(r)))
 }
 
+func eglWaitClient() bool {
+	r, _, _ := _eglWaitClient.Call()
+	return r != 0
+}
+
 // issue34474KeepAlive calls runtime.KeepAlive as a
 // workaround for golang.org/issue/34474.
 func issue34474KeepAlive(v interface{}) {