Fix architecture detection without --host

configure.ac

@@ -2,6 +2,8 @@ AC_INIT(dt_ctrl, git)
 
 AC_SUBST(HOSTSYS,["$ac_cv_env_host_alias_value"])
 AC_SUBST(BUILDSYS,["$ac_cv_env_build_alias_value"])
+AS_IF([test "$ac_cv_env_host_alias_value" == ""],[HOSTSYS=`uname -m`],[])
+
 AS_IF([echo "$HOSTSYS" | grep "arm"],[HAVE_ARM=1],[HAVE_ARM=0])
 
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