Shorten comparison.

configure.ac

@@ -120,8 +120,7 @@ dnl platforms is slow
 AC_CHECK_PROGS([MAKE], [$_cv_gnu_make_command gmake gnumake make])
 dnl maintainers need GNU make for the regeneration rules, so enforce that
 dnl
-AS_IF([test "x$_cv_gnu_make_command" = "x" \
-  && test x"$USE_MAINTAINER_MODE" = xyes],
+AS_IF([test "x${_cv_gnu_make_command}x$USE_MAINTAINER_MODE" = xxyes],
   [AC_MSG_FAILURE([maintainers need to use GNU make or compatible])])
 AC_PROG_MAKE_SET
 AC_PROG_INSTALL