Start on updating to Rust Nightly 1.39

[phase]

I have almost everything updated except for a few things.

hashmap_core relies on some internal allocation error enums that were recently changed. I've got a patch here but it still needs testing and such.

Other than that, I'm getting these odd errors:

error: unrecognized platform-specific intrinsic function: `x86_rdrand32_step`
  --> src/arch/x64/devices/rand/rdrand.rs:21:5
   |
21 |     fn x86_rdrand32_step() -> (u32, i32);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: unrecognized platform-specific intrinsic function: `x86_rdrand64_step`
  --> src/arch/x64/devices/rand/rdrand.rs:22:5
   |
22 |     fn x86_rdrand64_step() -> (u64, i32);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: unrecognized platform-specific intrinsic function: `x86_rdseed32_step`
  --> src/arch/x64/devices/rand/rdseed.rs:21:5
   |
21 |     fn x86_rdseed32_step() -> (u32, i32);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: unrecognized platform-specific intrinsic function: `x86_rdseed64_step`
  --> src/arch/x64/devices/rand/rdseed.rs:22:5
   |
22 |     fn x86_rdseed64_step() -> (u64, i32);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I'm not sure if this has to do with my system or not. I'm running Manjaro Linux.
I think this has something to do with the rand_core version. I upgraded it to 4.0 but the latest version, 5.0, brings a lot of API changes.

I'll try to work on this when I can!

[lachlansneff]

Those rand functions are "platform-intrinsics". Their names may have changed or they may have been removed.

[ids1024]

Is there a particular nightly that the current nebulet code is known to build on?