[flang][runtime] Support all non-ASCII characters in temporary path on Windows

If the path to the TEMP folder contains (non-ASCII) characters that cannot be
encoded in the current 8-bit locale of the user, openfile_mkstemp might fail
on Windows.
That is an unlikely scenario. But given that the path to the default TEMP
folder on Windows contains the Windows user name, it is still possible.

Use the wide character Windows API to avoid that (unlikely) issue.

Reviewed By: vzakhari

Differential Revision: https://reviews.llvm.org/D151571

Author: mmuetzel

flang/runtime/file.cpp

@@ -33,19 +33,19 @@ void OpenFile::set_path(OwningPtr<char> &&path, std::size_t bytes) {
 static int openfile_mkstemp(IoErrorHandler &handler) {
 #ifdef _WIN32
   const unsigned int uUnique{0};
-  // GetTempFileNameA needs a directory name < MAX_PATH-14 characters in length.
-  // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamea
-  char tempDirName[MAX_PATH - 14];
-  char tempFileName[MAX_PATH];
+  // GetTempFileNameW needs a directory name < MAX_PATH-14 characters in length.
+  // https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-gettempfilenamew
+  wchar_t tempDirName[MAX_PATH - 14];
+  wchar_t tempFileName[MAX_PATH];
   unsigned long nBufferLength{sizeof(tempDirName)};
-  nBufferLength = ::GetTempPathA(nBufferLength, tempDirName);
+  nBufferLength = ::GetTempPathW(nBufferLength, tempDirName);
   if (nBufferLength > sizeof(tempDirName) || nBufferLength == 0) {
     return -1;
   }
-  if (::GetTempFileNameA(tempDirName, "Fortran", uUnique, tempFileName) == 0) {
+  if (::GetTempFileNameW(tempDirName, L"Fortran", uUnique, tempFileName) == 0) {
     return -1;
   }
-  int fd{::_open(tempFileName, _O_CREAT | _O_BINARY | _O_TEMPORARY | _O_RDWR,
+  int fd{::_wopen(tempFileName, _O_CREAT | _O_BINARY | _O_TEMPORARY | _O_RDWR,
       _S_IREAD | _S_IWRITE)};
 #else
   char path[]{"/tmp/Fortran-Scratch-XXXXXX"};