Rollup merge of #98384 - rdzhaafar:fix-macos-rss-reporting, r=davidtwco,michaelwoerister

Fix RSS reporting on macOS

> 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:

```rust
...
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:

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

compiler/rustc_data_structures/src/profiling.rs

@@ -826,6 +826,24 @@ cfg_if! {
                 }
             }
         }
+    } else if #[cfg(target_os = "macos")] {
+        pub fn get_resident_set_size() -> Option<usize> {
+            use libc::{c_int, c_void, getpid, proc_pidinfo, proc_taskinfo, PROC_PIDTASKINFO};
+            use std::mem;
+            const PROC_TASKINFO_SIZE: c_int = mem::size_of::<proc_taskinfo>() as c_int;
+
+            unsafe {
+                let mut info: proc_taskinfo = mem::zeroed();
+                let info_ptr = &mut info as *mut proc_taskinfo as *mut c_void;
+                let pid = getpid() as c_int;
+                let ret = proc_pidinfo(pid, PROC_PIDTASKINFO, 0, info_ptr, PROC_TASKINFO_SIZE);
+                if ret == PROC_TASKINFO_SIZE {
+                    Some(info.pti_resident_size as usize)
+                } else {
+                    None
+                }
+            }
+        }
     } else if #[cfg(unix)] {
         pub fn get_resident_set_size() -> Option<usize> {
             let field = 1;