MongoDB 3.4's `openssl_fips` unconditionally references `openssl.FIPSModeSet` when SSL is being used with OpenSSL post-1.0: https://github.com/mongodb/mongo/blob/v3.4/src/mongo/gotools/common/db/openssl/openssl_fips.go#L21

However, its vendored version of `github.com/10gen/openssl` doesn't build its FIPS wrappers on Darwin: https://github.com/mongodb/mongo/blob/0d6a9242c11b99ddadcfb6e86a850b6ba487530a/src/mongo/gotools/vendor/src/github.com/10gen/openssl/fips.go#L2 This causes the build to fail on Darwin since the referenced function doesn't exist.

This doesn't seem to affect the 3.6 and 4.0 branches, which vendor a newer commit from this project which doesn't have the `+build !darwin` tag.