Add host_cpu_load_info on Apple

Snippet from `host_info.h`:

```
struct host_cpu_load_info {             /* number of ticks while running... */
    natural_t       cpu_ticks[CPU_STATE_MAX]; /* ... in the given mode */
};

typedef struct host_cpu_load_info       host_cpu_load_info_data_t;
typedef struct host_cpu_load_info       *host_cpu_load_info_t;
```

(backport <#3916>)
(cherry picked from commit f31fe2a)

Author: stepancheg

libc-test/semver/apple.txt

@@ -1983,6 +1983,9 @@ getxattr
 glob
 glob_t
 globfree
+host_cpu_load_info
+host_cpu_load_info_data_t
+host_cpu_load_info_t
 iconv
 iconv_close
 iconv_open

src/unix/bsd/apple/mod.rs

@@ -72,6 +72,11 @@ pub type ledger_array_t = *mut ::ledger_t;
 
 pub type iconv_t = *mut ::c_void;
 
+// mach/host_info.h
+pub type host_cpu_load_info_t = *mut host_cpu_load_info;
+pub type host_cpu_load_info_data_t = host_cpu_load_info;
+
+// mach/processor_info.h
 pub type processor_cpu_load_info_t = *mut processor_cpu_load_info;
 pub type processor_cpu_load_info_data_t = processor_cpu_load_info;
 pub type processor_basic_info_t = *mut processor_basic_info;
@@ -1189,6 +1194,11 @@ s! {
         pub tcpi_rxoutoforderbytes: u64,
         pub tcpi_rxretransmitpackets: u64,
     }
+
+    // mach/host_info.h
+    pub struct host_cpu_load_info {
+        pub cpu_ticks: [::natural_t; CPU_STATE_MAX as usize],
+    }
 }
 
 s_no_extra_traits! {