more gcc warnings

diff --git a/configure.ac b/configure.ac
index 19996fb5d1225d9b89d618516473be26c77d484a..fcd1ca4fef0e428b6ad189402d47218760036ee3 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -56,7 +56,7 @@ if test x"$GCC" = xyes; then
   # Wextra does not turn those on?
   flags="$flags -Wmissing-prototypes -Wpointer-arith -Wendif-labels"
   flags="$flags -Wdeclaration-after-statement -Wold-style-definition"
-  flags="$flags -Wstrict-prototypes"
+  flags="$flags -Wstrict-prototypes -Wundef -Wformat -Wnonnull"
   for f in $flags; do
     CFLAGS="$good_CFLAGS $warnings $f"
     AC_COMPILE_IFELSE([void foo(void){}], [warnings="$warnings $f"])