libobs: Introduce the concept of a Unix platform

This is a Unix-specific code. The only available platforms
at this point are the X11/GLX and X11/EGL platforms.

The concept of a platform display is also introduced. Again,
the only display that is set right now is the X11 display.

UI/obs-app.cpp

@@ -58,6 +58,11 @@
 #include <pthread.h>
 #endif
 
+#if !defined(_WIN32) && !defined(__APPLE__)
+#include <obs-nix-platform.h>
+#include <QX11Info>
+#endif
+
 #include <iostream>
 
 #include "ui-config.h"
@@ -1384,6 +1389,13 @@ bool OBSApp::OBSInit()
 
 	qRegisterMetaType<VoidFunc>();
 
+#if !defined(_WIN32) && !defined(__APPLE__)
+	obs_set_nix_platform(OBS_NIX_PLATFORM_X11_GLX);
+	if (QApplication::platformName() == "xcb") {
+		obs_set_nix_platform_display(QX11Info::display());
+	}
+#endif
+
 	if (!StartupOBS(locale.c_str(), GetProfilerNameStore()))
 		return false;