[PATCH] Various MINGW build fixes

[Jon TURNEY]

More hopefully uncontroversial fixes for building with the current MinGW-w64 toolchain.

app/xclock:
  No point in trying to use iconv if we don't have nl_langinfo

app/xhost:
  Move sethostent()/gethostent() stubs to avoid implicit-function-declaration warnings

app/xload:
  Use Windows load interface for Win32 build, as well as Cygwin
  Don't try to use [gs]et[ug]id on Win32

app/xset:
  Include unistd.h for usleep() if HAVE_USLEEP