build: detect and create AM_SILENT_RULES macro if needed

Older libs have problem with that:
configure.ac:17: warning: macro `AM_SILENT_RULES'
  not found in library
...
configure.ac:24: error: possibly undefined macro:
   AM_SILENT_RULES
Tested-by: NetDEF CI System <cisystem@netdef.org>

diff --git a/configure.ac b/configure.ac
index edd77b2b8ae22341573f2a1ed2fb89a31bea7e28..e01af9e55e2116f90c0844844c18c5e6d2734db5 100755 (executable)
--- a/configure.ac
+++ b/configure.ac
@@ -21,6 +21,7 @@ AC_CANONICAL_HOST()
 AC_CANONICAL_TARGET()
 
 AM_INIT_AUTOMAKE(1.6)
+m4_ifndef([AM_SILENT_RULES], [m4_define([AM_SILENT_RULES],[])])
 AM_SILENT_RULES([yes])
 AC_CONFIG_HEADERS(config.h)