Revert cargo update, but fails: cannot find function pthread_atfork…

… in crate `libc`

error[E0425]: cannot find function `pthread_atfork` in crate `libc`
   --> .cargo/registry/src/github.com-1ecc6299db9ec823/rand-0.6.5/src/rngs/adapter/reseeding.rs:320:28
    |
320 |             unsafe { libc::pthread_atfork(None, None, Some(fork_handler)) };
    |                            ^^^^^^^^^^^^^^ not found in `libc`

   Compiling quote v0.6.10
   Compiling syn v0.15.23
error: aborting due to previous error

For more information about this error, try `rustc --explain E0425`.
error: could not compile `rand`.
warning: build failed, waiting for other jobs to finish...
error: build failed

real	0m7.047s
user	0m20.843s
sys	0m2.494s

steven_blocks v0.0.1 (steven/blocks)
├── cgmath v0.17.0
│   ├── approx v0.3.2
│   │   └── num-traits v0.2.6
│   ├── num-traits v0.2.6 (*)
│   ├── rand v0.6.5
│   │   ├── libc v0.2.9