package/kmsxx: fix fmt dependency (needs wchar)

package/kmsxx: fix fmt dependency (needs wchar)

Propagate the fmt dependency on wchar.

Fixes:

 - http://autobuild.buildroot.net/results/814b0f9c3df0076791ca73579b844ef4d56f13c3

  [ 66%] Building CXX object CMakeFiles/fmt.dir/src/os.cc.o
  In file included from .../build/fmt-7.1.3/include/fmt/os.h:26,
                   from .../build/fmt-7.1.3/src/os.cc:13:
  .../build/fmt-7.1.3/include/fmt/format.h:1139:8: error: 'wstring' in namespace 'std' does not name a type
     std::wstring str() const { return {&buffer_[0], size()}; }
          ^~~~~~~

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>