Add support for the "fips140" mode of Go:
- https://go.dev/doc/security/fips140
- https://csrc.nist.gov/projects/cryptographic-module-validation-program/certificate/5247
You can build with `make fips140`, see the README changes for more info.
Some differences from the boringcrypto builds:
- We switch to using `go:linkname crypto/tls.aeadAESGCMTLS13`, which gives us the fips implementation for both `boringcrypto` and `fips140` modes. This means we also no longer need `-checklinkname=0`
- Go native `fips140` doesn't need CGO_ENABLED=1
- We decide if we should use the fips140 GCM at runtime, if `fips140.Enabled()` is true. If you use the `make release-fips140`, we build with build tag `fips140enforce` which ensures the binary is running with fips140 enabled and that only P256 / AES-GCM is being used. If you don't want this enforce mode, you can build without the build tag.
* add test for GOEXPERIMENT=boringcrypto
* fix NebulaCertificate.Sign
Set the PublicKey field in a more compatible way for the tests. The
current method grabs the public key from the certificate, but the
correct thing to do is to derive it from the private key. Either way
doesn't really matter as I don't think the Sign method actually even
uses the PublicKey field.
* assert boring
* cleanup tests
Wade Simmons