Add mach_error_string (and mach_error_t)

Author: stepancheg

libc-test/semver/apple.txt

@@ -1912,6 +1912,8 @@ lockf
 log2phys
 login_tty
 lutimes
+mach_error_string
+mach_error_t
 madvise
 malloc_default_zone
 malloc_good_size

src/unix/bsd/apple/mod.rs

@@ -58,6 +58,7 @@ pub type thread_inspect_t = ::mach_port_t;
 pub type thread_act_t = ::mach_port_t;
 pub type thread_act_array_t = *mut ::thread_act_t;
 pub type policy_t = ::c_int;
+pub type mach_error_t = ::kern_return_t;
 pub type mach_vm_address_t = u64;
 pub type mach_vm_offset_t = u64;
 pub type mach_vm_size_t = u64;
@@ -6202,6 +6203,8 @@ extern "C" {
     pub fn copyfile_state_get(s: copyfile_state_t, flags: u32, dst: *mut ::c_void) -> ::c_int;
     pub fn copyfile_state_set(s: copyfile_state_t, flags: u32, src: *const ::c_void) -> ::c_int;
 
+    pub fn mach_error_string(error_value: ::mach_error_t) -> *mut ::c_char;
+
     // Added in macOS 10.13
     // ISO/IEC 9899:2011 ("ISO C11") K.3.7.4.1
     pub fn memset_s(s: *mut ::c_void, smax: ::size_t, c: ::c_int, n: ::size_t) -> ::c_int;