Define `int128_t` and `uint128_t` in one place.

Change-Id: Ia93130aadf319eaba1b6f2ec2896a4c50d9e8ede
Reviewed-on: https://boringssl-review.googlesource.com/6975
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/internal.h b/crypto/internal.h
index 5574aab..714f207 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -188,6 +188,12 @@
 #endif
 
 
+#if !defined(_MSC_VER)
+typedef __int128_t int128_t;
+typedef __uint128_t uint128_t;
+#endif
+
+
 /* Constant-time utility functions.
  *
  * The following methods return a bitmask of all ones (0xff...f) for true and 0