test/bin: add checkflags to detect flag changes

This script can be used in a Makefile to detect flag changes
and to save the new flags in a file.

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

test/bin/checkflags

+#!/bin/sh
+# Author: Christian Couder <chriscool@tuxfamily.org>
+# MIT LICENSED
+
+if test "$#" -lt 3
+then
+    echo >&2 "usage $0 FILE VALUES MSG..."
+    exit 1
+fi
+
+FLAG_FILE="$1"
+FLAG_VALS="$2"
+shift
+shift
+FLAG_MSGS="$@"
+
+# Use x in front of tested values as flags could be
+# interpreted by "test" to be for itself.
+if test x"$FLAG_VALS" != x"$(cat "$FLAG_FILE" 2>/dev/null)"
+then
+    echo "$FLAG_MSGS"
+    echo "$FLAG_VALS" >"$FLAG_FILE"
+fi