Enable 2021 compatibility lints for all in-tree code

This just applies the suggested fixes from the compatibility warnings,
leaving any that are in practice spurious in. This is primarily intended to
provide a starting point to identify possible fixes to the migrations (e.g., by
avoiding spurious warnings).

A secondary commit cleans these up where they are false positives (as is true in
many of the cases).

1 files changed, 5 insertions, 2 deletions

diff --git a/compiler/rustc_codegen_llvm/src/back/lto.rs b/compiler/rustc_codegen_llvm/src/back/lto.rs
index f612785e5a4..fcb79c8332c 100644
--- a/compiler/rustc_codegen_llvm/src/back/lto.rs
+++ b/compiler/rustc_codegen_llvm/src/back/lto.rs
@@ -906,8 +906,11 @@ impl ThinLTOKeysMap {
     ) -> Self {
         let keys = iter::zip(modules, names)
             .map(|(module, name)| {
-                let key = build_string(|rust_str| unsafe {
-                    llvm::LLVMRustComputeLTOCacheKey(rust_str, module.identifier, data.0);
+                let key = build_string(|rust_str| {
+                    let _ = &data;
+                    unsafe {
+                        llvm::LLVMRustComputeLTOCacheKey(rust_str, module.identifier, data.0);
+                    }
                 })
                 .expect("Invalid ThinLTO module key");
                 (name.clone().into_string().unwrap(), key)