configure: inform the user when we're building sw/kms-dri

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/configure.ac b/configure.ac
index 633dcc4..eb69cc6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1983,6 +1983,7 @@
             fi
 
             if test "x$have_libdrm" = xyes; then
+                GALLIUM_WINSYS_DIRS="$GALLIUM_WINSYS_DIRS sw/kms-dri"
                 GALLIUM_TARGET_DIRS="$GALLIUM_TARGET_DIRS dri/kms-swrast"
             fi
             ;;