ntp sampler fails to build on musl libc (Alpine Linux)

[jirutka]

Describe the bug

ntp sampler fails to build on a system with musl libc (Alpine Linux):

error[E0425]: cannot find function `ntp_gettime` in crate `libc`
  --> src/samplers/ntp/mod.rs:94:37
   |
94 |         let status = unsafe { libc::ntp_gettime(&mut timeval) };
   |                                     ^^^^^^^^^^^ not found in `libc`

error[E0412]: cannot find type `ntptimeval` in crate `libc`
   --> src/samplers/ntp/mod.rs:128:34
    |
128 |   fn default_ntptimeval() -> libc::ntptimeval {
    |                                    ^^^^^^^^^^ help: a struct with a similar name exists: `timeval`
    | 
   ::: .cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/libc-0.2.82/src/unix/mod.rs:43:1
    |
43  | / s! {
44  | |     pub struct group {
45  | |         pub gr_name: *mut ::c_char,
46  | |         pub gr_passwd: *mut ::c_char,
...   |
195 | |     }
196 | | }
    | |_- similarly named struct `timeval` defined here

error[E0422]: cannot find struct, variant or union type `ntptimeval` in crate `libc`
   --> src/samplers/ntp/mod.rs:129:11
    |
129 |       libc::ntptimeval {
    |             ^^^^^^^^^^ help: a struct with a similar name exists: `timeval`
    | 
   ::: .cargo/registry/src/jackfan.us.kg-1ecc6299db9ec823/libc-0.2.82/src/unix/mod.rs:43:1
    |
43  | / s! {
44  | |     pub struct group {
45  | |         pub gr_name: *mut ::c_char,
46  | |         pub gr_passwd: *mut ::c_char,
...   |
195 | |     }
196 | | }
    | |_- similarly named struct `timeval` defined here

error: aborting due to 3 previous errors

To Reproduce
Steps to reproduce the behavior:

Build the project on Alpine Linux Edge.

1. apk add build-base cargo
2. wget https://github.com/twitter/rezolus/archive/v2.11.1.tar.gz && tar -xzf v2.11.1.tar.gz && cd rezolus-2.11.1
3. cargo build --release --locked

Expected behavior
The build should complete successfully.

Environment

• rust 1.51.0
• musl libc 1.2.2
• Alpine Linux Edge
• x86_64

Additional context
Add any other context about the problem here.

[brayniac]

Thanks for reporting.

Fixed by #218