Support: unlock Windows API support, switch to Windows 10 RS1+ APIs

This addresses a small window of in-atomicity in the rename support for
Windows. If the rename API is stressed sufficiently, it can run afoul of
the small window of opportunity where the destination file will not
exist. In Swift, this causes the `LockFileManager` to improperly handle
file locking for module compilation resulting in spurious failures as
the file file is failed to be read after writing due to multiple
processes overwriting the file and exposing the window constantly to the
scheduled process when building with `-num-threads` > for the Swift
driver.

The implementation of `llvm::sys::fs::rename` was changed in SVN r315079
(80e31f1) which even explicitly
identifies the issue:

~~~
This implementation is still not fully POSIX. Specifically in the case
where the destination file is open at the point when rename is called,
there will be a short interval of time during which the destination
file will not exist. It isn't clear whether it is possible to avoid
this using the Windows API.
~~~

Special thanks to Ben Barham for the discussions and help with analyzing
logging to track down this issue!

This API was introduced with Windows 10 RS1, and although there are LTSC
contracts that allow older versions to be supported still, the
mainstream support system has declared this release to be obsoleted. As
such, assuming that the OS is at least as new as this is reasonable.

Author: compnerd

llvm/include/llvm/Support/Windows/WindowsSupport.h

@@ -21,11 +21,13 @@
 #ifndef LLVM_SUPPORT_WINDOWSSUPPORT_H
 #define LLVM_SUPPORT_WINDOWSSUPPORT_H
 
+#if defined(__MINGW32__)
 // mingw-w64 tends to define it as 0x0502 in its headers.
 #undef _WIN32_WINNT
-
 // Require at least Windows 7 API.
 #define _WIN32_WINNT 0x0601
+#endif
+
 #define WIN32_LEAN_AND_MEAN
 #ifndef NOMINMAX
 #define NOMINMAX

llvm/lib/Support/Windows/Path.inc

@@ -466,13 +466,14 @@ static std::error_code rename_internal(HANDLE FromHandle, const Twine &To,
                                   (ToWide.size() * sizeof(wchar_t)));
   FILE_RENAME_INFO &RenameInfo =
       *reinterpret_cast<FILE_RENAME_INFO *>(RenameInfoBuf.data());
-  RenameInfo.ReplaceIfExists = ReplaceIfExists;
+  RenameInfo.Flags = FILE_RENAME_FLAG_POSIX_SEMANTICS
+                   | (ReplaceIfExists ? FILE_RENAME_FLAG_REPLACE_IF_EXISTS : 0);
   RenameInfo.RootDirectory = 0;
   RenameInfo.FileNameLength = ToWide.size() * sizeof(wchar_t);
   std::copy(ToWide.begin(), ToWide.end(), &RenameInfo.FileName[0]);
 
   SetLastError(ERROR_SUCCESS);
-  if (!SetFileInformationByHandle(FromHandle, FileRenameInfo, &RenameInfo,
+  if (!SetFileInformationByHandle(FromHandle, FileRenameInfoEx, &RenameInfo,
                                   RenameInfoBuf.size())) {
     unsigned Error = GetLastError();
     if (Error == ERROR_SUCCESS)