Make sure we have a C99 compiler

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@3785 d4fa192b-c00b-0410-8231-f00ffab90ce4

configure.ac

@@ -15,6 +15,10 @@ AM_INIT_AUTOMAKE([foreign])
 # Checks for programs.
 AC_GNU_SOURCE
 AC_PROG_CC
+AC_PROG_CC_STDC
+if test "x$ac_cv_prog_cc_c99" = xno; then
+  AC_MSG_ERROR([Could not find a C99 compatible compiler])
+fi
 AC_PROG_CPP
 AC_PROG_INSTALL
 AC_PROG_LIBTOOL