Don't disable stdin and stdout buffering on Windows

[amccarth]

Summary

Disabling buffering exposes a bug in the MS VS 2015 CRT implementation of fgets, where you sometimes have to hit Enter twice, depending on if the input had an odd or even number of characters.

This was hidden until a few days ago by the Python initialization which was re-enabling buffering on the streams. A few days ago, Enrico make the Python initialization on-demand, which exposed this problem.

[zturner]

I think you can probably leave buffering turned off for stdout and only do this change for stdin unless we find some other bug. AFAIK the problem is confined to stdin. I'd probably leave a comment in Driver::MainLoop() about why you're not disabling buffering on Windows though.

[amccarth]

In D19136#401888, @zturner wrote:

I think you can probably leave buffering turned off for stdout and only do this change for stdin unless we find some other bug. AFAIK the problem is confined to stdin. I'd probably leave a comment in Driver::MainLoop() about why you're not disabling buffering on Windows though.

Done. Re-running tests on Windows and will submit when they're done.

[amccarth]

rL266384

tools/driver/Driver.cpp

 Driver::MainLoop ()
 {
     if (::tcgetattr(STDIN_FILENO, &g_old_stdin_termios) == 0)
     {
         g_old_stdin_termios_is_valid = true;
         atexit (reset_stdin_termios);
     }
 
+#ifndef _MSC_VER
     ::setbuf (stdin, NULL);
     ::setbuf (stdout, NULL);
+#endif
 
     m_debugger.SetErrorFileHandle (stderr, false);
     m_debugger.SetOutputFileHandle (stdout, false);
     m_debugger.SetInputFileHandle (stdin, false); // Don't take ownership of STDIN yet...
 
     m_debugger.SetUseExternalEditor(m_option_data.m_use_external_editor);
 
     struct winsize window_size;

 
 int
 #ifdef WIN32
 wmain(int argc, wchar_t const *wargv[])
 #else
 main(int argc, char const *argv[])
 #endif
 {
-#ifdef _MSC_VER
-  // disable buffering on windows
-  setvbuf(stdout, NULL, _IONBF, 0);
-  setvbuf(stdin , NULL, _IONBF, 0);
-#endif
-
 #ifdef _WIN32
         // Convert wide arguments to UTF-8
         std::vector<std::string> argvStrings(argc);
         std::vector<const char *> argvPointers(argc);
         for (int i = 0; i != argc; ++i)
         {
             llvm::convertWideToUTF8(wargv[i], argvStrings[i]);
             argvPointers[i] = argvStrings[i].c_str();