configure: Fix build with automake < 1.11

Commit 86d30dea3c13d29ef8d39bc18db63a0441051975 broke building with older
automake versions with this error:

Makefile:769: *** Recursive variable am__v_YACC_ references itself (eventually).  Stop.

This patch fixes it. Fix stolen from xorg-macros.

Signed-off-by: Lauri Kasanen <cand@gmx.com>
diff --git a/configure.ac b/configure.ac
index 1e11b4e..3efef04 100644
--- a/configure.ac
+++ b/configure.ac
@@ -20,7 +20,8 @@
 # Support silent build rules, requires at least automake-1.11. Disable
 # by either passing --disable-silent-rules to configure or passing V=1
 # to make
-m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
+m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])],
+    [AC_SUBST([AM_DEFAULT_VERBOSITY], [1])])
 
 m4_ifdef([AM_PROG_AR], [AM_PROG_AR])