dmake.exe: Error code 129, while making 'Curve25519.o'

The problem lies with the symbol "OUT".
Consider this C program:

#include <windows.h>

int main(void) {
 int OUT = 7;
 return 0;
}
[download]

If you attempt to compile that program on Windows, you get:

try.c: In function 'main':
try.c:4:10: error: expected identifier or '(' before '=' token
  int OUT = 7;
          ^
[download]

I think that's a pretty good indication that OUT is a special symbol on Windows.
The program builds fine if windows.h is not included but, of course, windows.h is included for the xs file.

Simplest solution would be to replace the symbol "OUT" with something that's not going to clash.
(I'll add that to the bug report unless someone else beats me to it.)

Cheers,
Rob