Improve dependency management for lib/system/win32/* files. Instead of copying the

Improve dependency management for lib/system/win32/* files.  Instead of copying the
files from win32/* to platform/*, create one line files in platform that include the
corresponding file in win32.  This makes life much more enjoyable!

The cruel irony is that NTFS has hard links just like Unix, but there's no way to
get to them from the DOS prompt!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@19033 91177308-0d34-0410-b5e6-96231b3b80d8