API: Provide dummy halt() in the glue layer.

This fixes a demo app link failure on platforms configured with CONFIG_PANIC_HANG.

Signed-off-by: Rafal Jaworowski <raj@semihalf.com>

api_examples/libgenwrap.c

@@ -84,7 +84,12 @@ void do_reset (void)
 	ub_reset();
 }
 
-void *malloc(size_t len)
+void *malloc (size_t len)
 {
 	return NULL;
 }
+
+void hang (void)
+{
+	while (1) ;
+}