Dogfood 'str_split_once() with compiler/

compiler/rustc_target/src/lib.rs

@@ -15,6 +15,7 @@
 #![feature(never_type)]
 #![feature(associated_type_bounds)]
 #![feature(exhaustive_patterns)]
+#![feature(str_split_once)]
 
 #[macro_use]
 extern crate rustc_macros;

compiler/rustc_target/src/spec/apple_base.rs

@@ -54,10 +54,7 @@ fn macos_deployment_target() -> (u32, u32) {
     let deployment_target = env::var("MACOSX_DEPLOYMENT_TARGET").ok();
     let version = deployment_target
         .as_ref()
-        .and_then(|s| {
-            let mut i = s.splitn(2, '.');
-            i.next().and_then(|a| i.next().map(|b| (a, b)))
-        })
+        .and_then(|s| s.split_once('.'))
         .and_then(|(a, b)| a.parse::<u32>().and_then(|a| b.parse::<u32>().map(|b| (a, b))).ok());
 
     version.unwrap_or((10, 7))