Remove -Wall -Werror from the default CFLAGS.

Add --with-warn option to configure, making it easy to
select between a couple of predefined warning options.

Having all warnings on and treated as errors wasn't so good,
since different versions of gcc have different warnings.
There's no need to make it harder than it should be to build
btpd.

configure.ac

@@ -9,7 +9,7 @@ AC_CONFIG_FILES([Makefile btpd/Makefile misc/Makefile cli/Makefile])
 AC_PROG_CC
 AC_PROG_RANLIB
 
-CFLAGS="$CFLAGS -std=c99 -Wall -Werror"
+CFLAGS="$CFLAGS -std=c99"
 
 case $target_os in
      linux*)
@@ -40,6 +40,26 @@ AC_ARG_WITH(curlconf,
 ],
 [])
 
+AC_ARG_WITH(warn,
+[  --with-warn=level       select warning preset (no,all,allerr)],
+[
+    case $withval in
+    no)
+	;;
+    all)
+	CFLAGS="$CFLAGS -Wall"
+	;;
+    allerr)
+	CFLAGS="$CFLAGS -Wall -Werror"
+	;;
+    *)
+	echo "Warning preset \"$withval\" not recognized. See --help."
+	exit 1
+	;;
+    esac
+],
+[])
+
 old_LDFLAGS="$LDFLAGS"
 LDFLAGS="$LDFLAGS $event_LDFLAGS"
 AC_CHECK_LIB(event, event_init, :, echo Must have libevent; exit 1)