Rollup merge of rust-lang#59879 - ebarnard:patch-1, r=alexcrichton

Use SecRandomCopyBytes instead of /dev/urandom on MacOS

SecRandomCopyBytes is [available since MacOS 10.7](https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc) which is the minimum supported version and which was suggested in rust-lang#58901 (comment) is the earliest version currently in use.

This matches the behaviour of other platforms which have a random number generator syscall available.

src/libstd/build.rs

@@ -30,7 +30,7 @@ fn main() {
         println!("cargo:rustc-link-lib=resolv");
     } else if target.contains("apple-darwin") {
         println!("cargo:rustc-link-lib=System");
-
+        println!("cargo:rustc-link-lib=framework=Security");
         // res_init and friends require -lresolv on macOS/iOS.
         // See #41582 and http://blog.achernya.com/2013/03/os-x-has-silly-libsystem.html
         println!("cargo:rustc-link-lib=resolv");

src/libstd/sys/unix/rand.rs

@@ -12,6 +12,7 @@ pub fn hashmap_random_keys() -> (u64, u64) {
 }
 
 #[cfg(all(unix,
+          not(target_os = "macos"),
           not(target_os = "ios"),
           not(target_os = "openbsd"),
           not(target_os = "freebsd"),
@@ -99,7 +100,7 @@ mod imp {
     }
 }
 
-#[cfg(target_os = "ios")]
+#[cfg(any(target_os = "macos", target_os = "ios"))]
 mod imp {
     use crate::io;
     use crate::ptr;