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

@@ -88,3 +88,8 @@ void *malloc(size_t len)
 {
 	return NULL;
 }
+
+void hang (void)
+{
+	while (1) ;
+}