SHA-1 rework

SHA-1 rework

First, add new SHA-1 implementations that use the x86 and ARM SHA-1
intrinsics, so that these can be taken advantage of in Windows builds.

Second, replace sha1-ssse3.asm with an easier-to-maintain implementation
using intrinsics, and build a copy of it with AVX+BMI2 enabled.

Finally, now that better SHA-1 implementations are included, support for
OpenSSL's SHA-1 is no longer very useful, so remove it.

I considered going in the other direction: removing all SHA-1 code and
relying completely on external libraries.  Some issues with that are:

- Statically linking OpenSSL into libwim.dll on Windows increases the
  binary size by over 4x, even when using "no-autoalginit".

- OpenSSL has deprecated its easy-to-use SHA-1 API in favor of the EVP
  API, which is harder to use (everything can fail) and slower.

- Windows CryptoAPI is Windows-only (duh) and also has a complex, slow
  API where every function can fail, so that's not great either.

- SHA-1 is considered insecure these days, so it may be unwise to count
  on its continued support in crypto libraries into the future.

So, let's just do it ourselves...