check for WIN32 (needed by Mingw32)

crypto/bn/bn.h

diff --git a/crypto/bn/bn.h b/crypto/bn/bn.h
index d882261..009b0eb 100644
--- a/crypto/bn/bn.h
+++ b/crypto/bn/bn.h
@@ -89,7 +89,7 @@
  * For machines with only one compiler (or shared libraries), this should
  * be on.  Again this in only really a problem on machines
  * using "long long's", are 32bit, and are not using my assembler code. */
-#if defined(MSDOS) || defined(WINDOWS) || defined(linux)
+#if defined(MSDOS) || defined(WINDOWS) || defined(WIN32) || defined(linux)
 #define BN_DIV2W
 #endif