Fix Windows bug that doesn't happen under wine: stdin defaults to text mode,…

Fix Windows bug that doesn't happen under wine: stdin defaults to text mode, which of course breaks compiler plugins.

c++/src/kj/main.c++

@@ -32,6 +32,7 @@
 #if _WIN32
 #include <windows.h>
 #include <io.h>
+#include <fcntl.h>
 #else
 #include <sys/uio.h>
 #endif
@@ -63,6 +64,21 @@ void TopLevelProcessContext::exit() {
   _exit(exitCode);
 }
 
+#if _WIN32
+void setStandardIoMode(int fd) {
+  // Set mode to binary if the fd is not a console.
+  HANDLE handle = reinterpret_cast<HANDLE>(_get_osfhandle(fd));
+  DWORD consoleMode;
+  if (GetConsoleMode(handle, &consoleMode)) {
+    // It's a console.
+  } else {
+    KJ_SYSCALL(_setmode(fd, _O_BINARY));
+  }
+}
+#else
+void setStandardIoMode(int fd) {}
+#endif
+
 static void writeLineToFd(int fd, StringPtr message) {
   // Write the given message to the given file descriptor with a trailing newline iff the message
   // is non-empty and doesn't already have a trailing newline.  We use writev() to do this in a
@@ -186,6 +202,10 @@ void TopLevelProcessContext::increaseLoggingVerbosity() {
 // =======================================================================================
 
 int runMainAndExit(ProcessContext& context, MainFunc&& func, int argc, char* argv[]) {
+  setStandardIoMode(STDIN_FILENO);
+  setStandardIoMode(STDOUT_FILENO);
+  setStandardIoMode(STDERR_FILENO);
+
 #if !KJ_NO_EXCEPTIONS
   try {
 #endif