apps: add a little mkdir utility

apps/Makefile

@@ -1,4 +1,4 @@
-APPS := init sh uname uptime hello ps ls args cat stat su session date
+APPS := init sh uname uptime hello ps ls args cat stat su session date mkdir
 
 APPS_DIR := $(LUNA_ROOT)/apps
 APPS_SRC := $(APPS_DIR)/src

apps/src/mkdir.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <sys/stat.h>
+
+int main(int argc, char** argv)
+{
+    if (argc == 1)
+    {
+        fprintf(stderr, "Usage: %s [directory]", argv[0]);
+        return 1;
+    }
+
+    if (mkdir(argv[1], 0755) < 0)
+    {
+        perror("mkdir");
+        return 1;
+    }
+}