- The #ifdef mess used in patch-vhdtool.c is pretty hacky and there's
  likely a better way to deal with platform differences.

- Given the above, testing is also needed to make sure large files
  actually work on various platforms.

- Fix build on macOS: For some strange reason, buildlink isn't pulling
  in libuuid as a dep (despite the existence of `.buildlink_libuuid_done').

- Remove ONLY_FOR_PLATFORM: It'd probably build/work fine for macOS once the
  libuuid issue is reolved. And for 64-bit NetBSD it builds fine if we
  define lseek64 as lseek, but it hasn't been tested or verified if that's
  the correct thing to do.

- Write a proper DESCR so that it isn't just a copy of COMMENT.

- See if `converters' is the best CATEGORY for this kind of tool.
