Fix incompatible pointer type in Windows code

[illwieckz]

Fixes:

nacl_host_dir.c:43:30: error: passing argument 1 of 'FindFirstFileA' from incompatible pointer type [-Wincompatible-pointer-types]
   43 |   d->handle = FindFirstFile(d->pattern, &d->find_data);
      |                             ~^~~~~~~~~
      |                              |
      |                              wchar_t * {aka short unsigned int *}

nacl_host_dir.c:220:34: error: passing argument 2 of 'FindNextFileA' from incompatible pointer type [-Wincompatible-pointer-types]
  220 |     if (!FindNextFile(d->handle, &d->find_data)) {
      |                                  ^~~~~~~~~~~~~
      |                                  |
      |                                  WIN32_FIND_DATAW *

I reproduced it with MinGW from Debian 13.2 Trixie.
I didn't reproduced it with MinGW from Ubuntu 24.04.4 Noble.

I noticed it while working on implementing the NaCl loader build in Dæmon's external deps:

• Rework external_deps for Saigo and CMake-based NaCL rebuild Daemon#1986