Invalidate process UID/GID-related command options on Windows.

Windows uses a different process security model and does not have
a concept of process UID or GID.  This patch makes these options
invalid on Windows.  Attempting to specify these options when the
current platform is Windows will generate an error.

Reviewed by: Jim Ingham
Differential Revision: http://reviews.llvm.org/D4373

llvm-svn: 212500