Detect when primusrun/optirun is in use

It seems that bumblebee doesn't like us creating multiple GL contexts
to avoid this we now detect whether we're running with this software
and don't do anything.

platform/x11/os_x11.cpp

@@ -243,8 +243,37 @@ Error OS_X11::initialize(const VideoMode &p_desired, int p_video_driver, int p_a
 // maybe contextgl wants to be in charge of creating the window
 #if defined(OPENGL_ENABLED)
 	if (getenv("DRI_PRIME") == NULL) {
-		print_verbose("Detecting GPUs, set DRI_PRIME in the environment to override GPU detection logic.");
-		int use_prime = detect_prime();
+		int use_prime = -1;
+
+		if (getenv("PRIMUS_DISPLAY") ||
+				getenv("PRIMUS_libGLd") ||
+				getenv("PRIMUS_libGLa") ||
+				getenv("PRIMUS_libGL") ||
+				getenv("PRIMUS_LOAD_GLOBAL") ||
+				getenv("BUMBLEBEE_SOCKET")) {
+
+			print_verbose("Optirun/primusrun detected. Skipping GPU detection");
+			use_prime = 0;
+		}
+
+		if (getenv("LD_LIBRARY_PATH")) {
+			String ld_library_path(getenv("LD_LIBRARY_PATH"));
+			Vector<String> libraries = ld_library_path.split(":");
+
+			for (int i = 0; i < libraries.size(); ++i) {
+				if (FileAccess::exists(libraries[i] + "/libGL.so.1") ||
+						FileAccess::exists(libraries[i] + "/libGL.so")) {
+
+					print_verbose("Custom libGL override detected. Skipping GPU detection");
+					use_prime = 0;
+				}
+			}
+		}
+
+		if (use_prime == -1) {
+			print_verbose("Detecting GPUs, set DRI_PRIME in the environment to override GPU detection logic.");
+			use_prime = detect_prime();
+		}
 
 		if (use_prime) {
 			print_line("Found discrete GPU, setting DRI_PRIME=1 to use it.");