wasapi: try to satisfy both mingw and msvc

Fix-up for previous commit, hopefully.
diff --git a/sys/wasapi/gstwasapiutil.c b/sys/wasapi/gstwasapiutil.c
index c689f50..5563ee7 100644
--- a/sys/wasapi/gstwasapiutil.c
+++ b/sys/wasapi/gstwasapiutil.c
@@ -32,6 +32,7 @@
 #if defined(_MSC_VER)
 #include <functiondiscoverykeys_devpkey.h>
 #elif !defined(PKEY_Device_FriendlyName)
+#include <initguid.h>
 #include <propkey.h>
 DEFINE_PROPERTYKEY (PKEY_Device_FriendlyName, 0xa45c254e, 0xdf1c, 0x4efd, 0x80,
     0x20, 0x67, 0xd1, 0x46, 0xa8, 0x50, 0xe0, 14);
diff --git a/sys/wasapi/gstwasapiutil.h b/sys/wasapi/gstwasapiutil.h
index 4fa2e08..235db0a 100644
--- a/sys/wasapi/gstwasapiutil.h
+++ b/sys/wasapi/gstwasapiutil.h
@@ -25,7 +25,9 @@
 #include <gst/audio/gstaudiosrc.h>
 #include <gst/audio/gstaudiosink.h>
 
+#ifdef _MSC_VER
 #include <initguid.h>
+#endif
 #include <mmdeviceapi.h>
 #include <audioclient.h>