Windows build fixes.

Windows doesn't have ssize_t, sadly. There's SSIZE_T, but defining an
OPENSSL_SSIZE_T seems worse than just using an int.

Change-Id: I09bb5aa03f96da78b619e551f92ed52ce24d9f3f
Reviewed-on: https://boringssl-review.googlesource.com/1352
Reviewed-by: Adam Langley <agl@google.com>
22 files changed