Implement utime() along with a naive /bin/touch.

This synchronous approach to inodes is silly, obviously. I need to rework
it so that the in-memory CoreInode object is the canonical inode, and then
we just need a sync() that flushes pending changes to disk.

LibC/utime.cpp

@@ -0,0 +1,14 @@
+#include <utime.h>
+#include <errno.h>
+#include <Kernel/Syscall.h>
+
+extern "C" {
+
+int utime(const char* pathname, const struct utimbuf* buf)
+{
+    int rc = Syscall::invoke(Syscall::SC_utime, (dword)pathname, (dword)buf);
+    __RETURN_WITH_ERRNO(rc, rc, -1);
+}
+
+}
+