utils/diffconfig: add diffconfig utility

Diffconfig is a simple utility for comparing two configuration files.
See usage in the script for more info.

Borrowed from the Linux kernel source code and adapted to Buildroot.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/DEVELOPERS b/DEVELOPERS
index 7dcc95b..1a6a31f 100644
--- a/DEVELOPERS
+++ b/DEVELOPERS
@@ -1014,6 +1014,9 @@
 N:	Marcin Nowakowski <marcin.nowakowski@imgtec.com>
 F:	package/libkcapi/
 
+N:	Marcus Folkesson <marcus.folkesson@gmail.com>
+F:	utils/diffconfig
+
 N:	Marek Belisko <marek.belisko@open-nandra.com>
 F:	package/libatasmart/
 F:	package/polkit/