configure: correctly autodetect xvmc/vdpau/omx

Commit e62b7d38a1d (configure: autodetect video state-trackers
when non swrast driver is present) added a check that caused
the autodetection to be omitted when we have the swrast gallium
driver. Whereas it should have skipped the VL targets when only
swrast was selected.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79907
Cc: "10.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
diff --git a/configure.ac b/configure.ac
index d897ac6..390adaa 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1393,7 +1393,7 @@
 dnl
 dnl Gallium G3DVL configuration
 dnl
-if test -n "$with_gallium_drivers" && ! echo "$with_gallium_drivers" | grep -q 'swrast'; then
+if test -n "$with_gallium_drivers" -a "x$with_gallium_drivers" != xswrast; then
     if test "x$enable_xvmc" = xauto; then
 	PKG_CHECK_EXISTS([xvmc], [enable_xvmc=yes], [enable_xvmc=no])
     fi