Support for platforms that we don't support FIPS on doesn't need to be
in the module. Also, functions for dealing with whether fork-unsafe
buffering is enabled are left out because they aren't implementing any
cryptography and they use global r/w state, making their inclusion
painful.

Change-Id: I71a0123db6f5449e9dfc7ec7dea0944428e661aa
Reviewed-on: https://boringssl-review.googlesource.com/15084
Reviewed-by: Adam Langley <agl@google.com>

This isn't actually used yet, but implements CTR-DRBG from SP 800-90Ar1.
Specifically, it always uses AES-256 and no derivation function.

Change-Id: Ie82b829590226addd7c165eac410a5d584858bfd
Reviewed-on: https://boringssl-review.googlesource.com/14891
Reviewed-by: Adam Langley <agl@google.com>