runqemu: force software x11 renderer for SDL when GL is not in use

If libsdl is configured with opengl enabled, it will try to use GL
renderers to open a window even if qemu doesn't use virgl. Setting
the environment variable forces a software X11 renderer, which is the
same one used when libsdl has opengl switched off. This avoids
needlessly loading the GL libraries and drivers from the host.

(From OE-Core rev: 73b75f5ff6c0b5333898fa340f4d9e2e5111fdef)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -448,6 +448,9 @@ class BaseConfig(object):
                 logger.setLevel(logging.ERROR)
                 sys.argv.remove(quiet)
 
+        if 'gl' not in sys.argv[1:] and 'gl-es' not in sys.argv[1:]:
+            os.environ['SDL_RENDER_DRIVER'] = 'software'
+
         unknown_arg = ""
         for arg in sys.argv[1:]:
             if arg in self.fstypes + self.vmtypes + self.wictypes: