Fix inferior's i/o connections to its console window on Windows 7

[amccarth]

Summary

Passing NULL for the standard handles is documented to do the right thing, but it doesn't work on Windows 7. However, passing the result of GetStdHandle does seem to work, and is recommended in this MSDN article, which specifically talks about overriding just some of the i/o handles in a new process with its own console window: https://support.microsoft.com/en-us/kb/190351 .

Can you patch this in and confirm that it still works on newer versions of Windows?

[zturner]

source/Host/windows/ProcessLauncherWindows.cpp

37–39

I think this would be a little better if we change the implementation of GetStdioHandle() to just return the right thing.

[amccarth]

source/Host/windows/ProcessLauncherWindows.cpp

37–39

I had started down that path, but ended up here because the caller doesn't otherwise know if it should close the handle.

[Eugene.Zelenko]

Committed in r238629.

source/Host/windows/ProcessLauncherWindows.cpp

ProcessLauncherWindows::LaunchProcess(const ProcessLaunchInfo &launch_info, Error &error)
     PROCESS_INFORMATION pi = {0};
 
     HANDLE stdin_handle = GetStdioHandle(launch_info, STDIN_FILENO);
     HANDLE stdout_handle = GetStdioHandle(launch_info, STDOUT_FILENO);
     HANDLE stderr_handle = GetStdioHandle(launch_info, STDERR_FILENO);
 
     startupinfo.cb = sizeof(startupinfo);
     startupinfo.dwFlags |= STARTF_USESTDHANDLES;
-    startupinfo.hStdError = stderr_handle;
-    startupinfo.hStdInput = stdin_handle;
-    startupinfo.hStdOutput = stdout_handle;
+    startupinfo.hStdError  = stderr_handle ? stderr_handle : ::GetStdHandle(STD_ERROR_HANDLE);
+    startupinfo.hStdInput  = stdin_handle  ? stdin_handle  : ::GetStdHandle(STD_INPUT_HANDLE);
+    startupinfo.hStdOutput = stdout_handle ? stdout_handle : ::GetStdHandle(STD_OUTPUT_HANDLE);
 
     const char *hide_console_var = getenv("LLDB_LAUNCH_INFERIORS_WITHOUT_CONSOLE");
     if (hide_console_var && llvm::StringRef(hide_console_var).equals_lower("true"))
     {
         startupinfo.dwFlags |= STARTF_USESHOWWINDOW;
         startupinfo.wShowWindow = SW_HIDE;
     }