no_std is broken (using with sgx)

[brenzi]

When I use this crate within a sgx enclave (https://github.com/baidu/rust-sgx-sdk)
I get:

error: duplicate lang item in crate `std`: `f32_runtime`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `std`: `f64_runtime`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `std`: `panic_impl`.
  |
  = note: first defined in crate `sgx_tstd`.

error: duplicate lang item in crate `std`: `oom`.
  |
  = note: first defined in crate `sgx_trts`.

Cargo.toml:

...
blake2-rfc = { version = "0.2.18", default-features = false}
...

[brenzi]

guess it's a problem wit ha dependency arrayvec:
https://github.com/bluss/arrayvec/blob/fd4a6469b9505109aa8a0539dbc7d36641ce0617/src/lib.rs#L34

[brenzi]

reported upstream: bluss/arrayvec#122

[brenzi]

arrayvec is innocent. problem must lie somewhere else