mesa: Enable subdir-objects globally.

Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/configure.ac b/configure.ac
index ddc757e..af61aa2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -44,7 +44,7 @@
 AC_CONFIG_AUX_DIR([bin])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CANONICAL_SYSTEM
-AM_INIT_AUTOMAKE([foreign tar-ustar dist-xz])
+AM_INIT_AUTOMAKE([foreign tar-ustar dist-xz subdir-objects])
 
 dnl We only support native Windows builds (MinGW/MSVC) through SCons.
 case "$host_os" in