Add a way to initialize VFS globals.

This is needed since the kernel loader doesn't even zero out bss,
much less call any static constructors.

VirtualFileSystem/VirtualFileSystem.h

@@ -14,6 +14,8 @@ class FileSystem;
 
 class VirtualFileSystem {
 public:
+    static void initializeGlobals();
+
     struct Node {
         InodeIdentifier inode;