The changes to delocate.go are needed because modes/ does things like
return the address of a module function. Both of these need to be
changed from referencing the GOT to using local symbols.

Rather than testing whether |ghash| is |gcm_ghash_avx|, we can just keep
that information in a flag.

The test for |aesni_ctr32_encrypt_blocks| is more problematic, but I
believe that it's superfluous and can be dropped: if you passed in a
stream function that was semantically different from
|aesni_ctr32_encrypt_blocks| you would already have a bug because
|CRYPTO_gcm128_[en|de]crypt_ctr32| will handle a block at the end
themselves, and assume a big-endian, 32-bit counter anyway.

Change-Id: I68a84ebdab6c6006e11e9467e3362d7585461385
Reviewed-on: https://boringssl-review.googlesource.com/15064
Reviewed-by: Adam Langley <agl@google.com>