avcodec/nvenc: fix double defined GUID on cygwin

compat/nvenc/nvEncodeAPI.h

@@ -77,7 +77,7 @@ extern "C" {
 typedef RECT NVENC_RECT;
 #else
 // =========================================================================================
-#ifndef GUID
+#if !defined(GUID) && !defined(GUID_DEFINED)
 /*!
  * \struct GUID
  * Abstracts the GUID structure for non-windows platforms.

libavcodec/nvenc.h

@@ -19,6 +19,13 @@
 #ifndef AVCODEC_NVENC_H
 #define AVCODEC_NVENC_H
 
+#if CONFIG_D3D11VA
+#define COBJMACROS
+#include "libavutil/hwcontext_d3d11va.h"
+#else
+typedef void ID3D11Device;
+#endif
+
 #include "compat/nvenc/nvEncodeAPI.h"
 
 #include "config.h"
@@ -27,13 +34,6 @@
 #include "libavutil/fifo.h"
 #include "libavutil/opt.h"
 
-#if CONFIG_D3D11VA
-#define COBJMACROS
-#include "libavutil/hwcontext_d3d11va.h"
-#else
-typedef void ID3D11Device;
-#endif
-
 #include "avcodec.h"
 
 #define MAX_REGISTERED_FRAMES 64