Add memset_s on apple OSX

Author: niluxv

libc-test/semver/apple.txt

@@ -1619,6 +1619,7 @@ mach_timebase_info_data_t
 madvise
 max_align_t
 mcontext_t
+memset_s
 mincore
 mkdirat
 mkstemps

src/unix/bsd/apple/mod.rs

@@ -3843,6 +3843,10 @@ extern "C" {
         dst: *const ::c_char,
         flags: u32,
     ) -> ::c_int;
+
+    // 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;
 }
 
 #[link(name = "iconv")]