Adopt let else in more places

compiler/rustc_codegen_llvm/src/back/archive.rs

@@ -310,10 +310,7 @@ impl<'a> LlvmArchiveBuilder<'a> {
             if let Some(archive) = self.src_archive() {
                 for child in archive.iter() {
                     let child = child.map_err(string_to_io_error)?;
-                    let child_name = match child.name() {
-                        Some(s) => s,
-                        None => continue,
-                    };
+                    let Some(child_name) = child.name() else { continue };
                     if removals.iter().any(|r| r == child_name) {
                         continue;
                     }

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -826,20 +826,14 @@ pub(crate) unsafe fn codegen(
                 let input =
                     unsafe { slice::from_raw_parts(input_ptr as *const u8, input_len as usize) };
 
-                let input = match str::from_utf8(input) {
-                    Ok(s) => s,
-                    Err(_) => return 0,
-                };
+                let Ok(input) = str::from_utf8(input) else { return 0 };
 
                 let output = unsafe {
                     slice::from_raw_parts_mut(output_ptr as *mut u8, output_len as usize)
                 };
                 let mut cursor = io::Cursor::new(output);
 
-                let demangled = match rustc_demangle::try_demangle(input) {
-                    Ok(d) => d,
-                    Err(_) => return 0,
-                };
+                let Ok(demangled) = rustc_demangle::try_demangle(input) else { return 0 };
 
                 if write!(cursor, "{:#}", demangled).is_err() {
                     // Possible only if provided buffer is not big enough