Fix RSS reporting on macOS

[rdzhaafar]

NOTE: This is a duplicate of #98164, which I closed because I borked my rustc fork

Currently, rustc_data_structures::profiling::get_resident_set_size() always returns None on macOS. This is because
macOS does not implement procfs used in the unix version of the function:

...
else if #[cfg(unix)] {
        pub fn get_resident_set_size() -> Option<usize> {
            let field = 1;
            let contents = fs::read("/proc/self/statm").ok()?;
            let contents = String::from_utf8(contents).ok()?;
            let s = contents.split_whitespace().nth(field)?;
            let npages = s.parse::<usize>().ok()?;
            Some(npages * 4096)
        }
...

The proposed solution uses libproc, and more specifically proc_pidinfo, which has been available on macOS since 10.5 if the function signature inside libproc.h is to be believed:

int proc_pidinfo(int pid, int flavor, uint64_t arg, void *buffer, int buffersize) __OSX_AVAILABLE_STARTING(__MAC_10_5, __IPHONE_2_0);

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @davidtwco (or someone else) soon.

Please see the contribution instructions for more information.

[davidtwco]

This seems reasonable to me but I'm not familiar with this API so I'll get a second opinion.

[davidtwco]

r? @michaelwoerister

[michaelwoerister]

Looks good to me. Thanks, @rdzhaafar!

@bors r=davidtwco,michaelwoerister

[bors]

📌 Commit c416307 has been approved by davidtwco,michaelwoerister