Use as_deref in compiler (but only where it makes sense)

Author: WaffleLapkin

build_system/utils.rs

@@ -104,5 +104,5 @@ pub(crate) fn copy_dir_recursively(from: &Path, to: &Path) {
 }
 
 pub(crate) fn is_ci() -> bool {
-    env::var("CI").as_ref().map(|val| &**val) == Ok("true")
+    env::var("CI").as_deref() == Ok("true")
 }

src/config.rs

@@ -2,7 +2,7 @@ use std::env;
 use std::str::FromStr;
 
 fn bool_env_var(key: &str) -> bool {
-    env::var(key).as_ref().map(|val| &**val) == Ok("1")
+    env::var(key).as_deref() == Ok("1")
 }
 
 /// The mode to use for compilation.