Fix Win32ErrorMessage on Unicode build

src/google/protobuf/compiler/subprocess.cc

@@ -261,11 +261,11 @@ string Subprocess::Win32ErrorMessage(DWORD error_code) {
   char* message;
 
   // WTF?
-  FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER |
+  FormatMessageA(FORMAT_MESSAGE_ALLOCATE_BUFFER |
                  FORMAT_MESSAGE_FROM_SYSTEM |
                  FORMAT_MESSAGE_IGNORE_INSERTS,
                  NULL, error_code, 0,
-                (LPTSTR)&message,  // NOT A BUG!
+                 (LPSTR)&message,  // NOT A BUG!
                  0, NULL);
 
   string result = message;