Renderer: Support running under Wayland or KMS

Ignore an error from GLEW in order to run natively under Wayland
(instead of going through XWayland) on Linux, or to run directly on top
of KMS/DRM.

Pioneer can be forced to run with Wayland like this:
SDL_VIDEODRIVER=wayland ./pioneer

Pioneer can be forced to run with KMS/DRM like this:
SDL_VIDEODRIVER=KMSDRM ./pioneer

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

src/graphics/opengl/RendererGL.cpp

@@ -173,8 +173,19 @@ namespace Graphics {
 	{
 		PROFILE_SCOPED()
 		glewExperimental = true;
-		GLenum glew_err;
-		if ((glew_err = glewInit()) != GLEW_OK)
+
+		const char *sdl_driver = SDL_GetCurrentVideoDriver();
+		Log::Info("SDL video driver used: {}", sdl_driver);
+
+		GLenum glew_err = glewInit();
+#ifdef GLEW_ERROR_NO_GLX_DISPLAY
+		if (glew_err == GLEW_ERROR_NO_GLX_DISPLAY
+		    && (!strcmp(sdl_driver, "wayland") || !strcmp(sdl_driver, "KMSDRM"))) {
+			Log::Info("Ignoring GLEW_ERROR_NO_GLX_DISPLAY as the video backend does not support GLX.");
+			glew_err = GLEW_OK;
+		}
+#endif
+		if (glew_err != GLEW_OK)
 			Error("GLEW initialisation failed: %s", glstr_to_str(glewGetErrorString(glew_err)));
 
 		// pump this once as glewExperimental is necessary but spews a single error