[tlbuild] mendexk test failure on Cygwin

[Akira Kakuto]

Dear Ken,

> The following patch fixes the problem for me, but I don't know why it should be platform-specific:

Do you have 4 (32bit) or 8 (64bit) in the following?
Here I have 4096 (very old mingw32 gcc 3.4.5).
If char *p = buff;
sizeof(p) is 4 or 8.

#include <stdio.h>
#define BUFFERLEN 4096
int main(void)
{
  char buff[BUFFERLEN];

  printf("%d\n", sizeof(buff));
  return 0;
}

Best,
Akira