Rollup merge of #80944 - LingMan:map_or, r=nagisa

Use Option::map_or instead of `.map(..).unwrap_or(..)`

``@rustbot`` modify labels +C-cleanup +T-compiler

compiler/rustc_driver/src/lib.rs

@@ -1236,7 +1236,7 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str) {
     }
 
     // If backtraces are enabled, also print the query stack
-    let backtrace = env::var_os("RUST_BACKTRACE").map(|x| &x != "0").unwrap_or(false);
+    let backtrace = env::var_os("RUST_BACKTRACE").map_or(false, |x| &x != "0");
 
     let num_frames = if backtrace { None } else { Some(2) };