coccinelle: add test for banned function

The added semantic patch will trigger an error if banned functions
are used.

qa/coccinelle/banned-functions.cocci

@@ -0,0 +1,17 @@
+@banned@
+identifier func ~= "^\(sprintf\|strcat\|strcpy\)$";
+position p1;
+@@
+
+<+...
+func(...)@p1
+...+>
+
+@ script:python @
+p1 << banned.p1;
+func << banned.func;
+@@
+
+print "Banned function %s() used at %s:%s" % (func, p1[0].file, p1[0].line)
+import sys
+sys.exit(1)