[PATCH] Various MinGW build fixes

[Jon TURNEY]

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

app/xkbcomp:
  Define WIN32_LEAN_AND_MEAN when building on Win32

lib/libICE:
  Include process.h for getpid() on Win32

lib/libSM:
  Include process.h for getpid() on Win32

lib/libXaw:
  Include <unistd.h>

lib/libXdmcp:
  Link with winsock library for socket functions on MinGW

lib/libXmu:
  Include <direct.h> for _getdrives() on Win32
  Remove pointless X_NOT_POSIX

lib/libXt:
  Include process.h for getpid() on Win32
  Include direct.h header for _getdrives() on Win32