Auto merge of #15652 - servo:nolibc, r=nox

Remove usage of unstable libc crate.

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- [ ] These changes fix #__ (github issue number if applicable).

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support/rust-task_info/src/lib.rs

@@ -10,9 +10,5 @@
 #![crate_name = "task_info"]
 #![crate_type = "rlib"]
 
-#![feature(libc)]
-
-extern crate libc;
-
 pub mod task_basic_info;
 

support/rust-task_info/src/task_basic_info.rs

@@ -10,7 +10,10 @@
 //! Interface to the measurements in the task_basic_info struct, gathered by
 //! invoking `task_info()` with the `TASK_BASIC_INFO` flavor.
 
-use libc::{c_int, size_t};
+use std::os::raw::c_int;
+
+#[allow(non_camel_case_types)]
+type size_t = usize;
 
 /// Obtains task_basic_info::virtual_size.
 pub fn virtual_size() -> Option<usize> {