Revert "tools: disable building qemu-trad per default"

Unfortunately this breaks the gitlab CI.  See mails on-list.

This reverts commit ce309942c7.

tools/configure.ac

@@ -120,7 +120,18 @@ AC_SUBST(LINUX_BACKEND_MODULES)
 
 AC_ARG_ENABLE([qemu-traditional],
     AS_HELP_STRING([--enable-qemu-traditional],
-                   [Enable qemu traditional device model, (DEFAULT is off)]))
+                   [Enable qemu traditional device model, (DEFAULT is on for Linux or NetBSD x86, otherwise off)]),,[
+    case "$host_cpu" in
+        i[[3456]]86|x86_64)
+           enable_qemu_traditional="yes";;
+        *) enable_qemu_traditional="no";;
+    esac
+    case "$host_os" in
+        freebsd*)
+           enable_qemu_traditional="no";;
+    esac
+
+])
 AS_IF([test "x$enable_qemu_traditional" = "xyes"], [
 AC_DEFINE([HAVE_QEMU_TRADITIONAL], [1], [Qemu traditional enabled])
     qemu_traditional=y],[