Fix issue #43: Errors building with mingw-w64 toolchain.

Author: Vincent Couvert

src/MIDataTypes.h

@@ -17,6 +17,8 @@
 // Windows headers:
 #ifdef _WIN32
 
+#include <windows.h>
+
 // Debugging:
 #ifdef _DEBUG
 #include <crtdbg.h>

src/Platform.h

@@ -7,7 +7,7 @@
 //===----------------------------------------------------------------------===//
 #pragma once
 
-#if defined(_MSC_VER)
+#if defined(_WIN32)
 
 #include <inttypes.h>
 #include <io.h>
@@ -45,7 +45,9 @@ struct termios {
   speed_t c_ospeed; // output speed
 };
 
+#if !defined(__MINGW32__) || !defined(_PID_T_) || defined(NO_OLDNAMES)
 typedef long pid_t;
+#endif
 
 #define STDIN_FILENO 0
 #define PATH_MAX 32768