Resolve all warnings in run-coverage tests

When one of these tests fails, any compiler warnings will be printed to the
console, which makes it harder to track down the actual reason for failure.

(The outstanding warnings were found by temporarily adding `-Dwarnings` to the
compiler arguments for `RunCoverage` in `src/tools/compiletest/src/runtest.rs`.)

Author: Zalathar

tests/run-coverage/async2.coverage

@@ -1,11 +1,5 @@
    LL|       |// compile-flags: --edition=2018
    LL|       |
-   LL|       |use core::{
-   LL|       |    future::Future,
-   LL|       |    marker::Send,
-   LL|       |    pin::Pin,
-   LL|       |};
-   LL|       |
    LL|      1|fn non_async_func() {
    LL|      1|    println!("non_async_func was covered");
    LL|      1|    let b = true;

tests/run-coverage/async2.rs

@@ -1,11 +1,5 @@
 // compile-flags: --edition=2018
 
-use core::{
-    future::Future,
-    marker::Send,
-    pin::Pin,
-};
-
 fn non_async_func() {
     println!("non_async_func was covered");
     let b = true;

tests/run-coverage/auxiliary/unused_mod_helper.rs

@@ -1,3 +1,4 @@
+#[allow(dead_code)]
 pub fn never_called_function() {
     println!("I am never called");
 }

tests/run-coverage/auxiliary/used_crate.rs

@@ -42,6 +42,7 @@ pub fn unused_function() {
     }
 }
 
+#[allow(dead_code)]
 fn unused_private_function() {
     let is_true = std::env::args().len() == 1;
     let mut countdown = 2;

tests/run-coverage/auxiliary/used_inline_crate.rs

@@ -71,6 +71,7 @@ pub fn unused_function() {
 }
 
 #[inline(always)]
+#[allow(dead_code)]
 fn unused_private_function() {
     let is_true = std::env::args().len() == 1;
     let mut countdown = 2;

tests/run-coverage/closure_macro_async.coverage

@@ -42,7 +42,7 @@
    LL|       |
    LL|       |#[no_coverage]
    LL|       |fn main() {
-   LL|       |    executor::block_on(test());
+   LL|       |    executor::block_on(test()).unwrap();
    LL|       |}
    LL|       |
    LL|       |mod executor {

tests/run-coverage/closure_macro_async.rs

@@ -41,7 +41,7 @@ pub async fn test() -> Result<(), String> {
 
 #[no_coverage]
 fn main() {
-    executor::block_on(test());
+    executor::block_on(test()).unwrap();
 }
 
 mod executor {

tests/run-coverage/dead_code.coverage

@@ -1,4 +1,4 @@
-   LL|       |#![allow(unused_assignments, unused_variables)]
+   LL|       |#![allow(dead_code, unused_assignments, unused_variables)]
    LL|       |
    LL|      0|pub fn unused_pub_fn_not_in_library() {
    LL|      0|    // Initialize test constants in a way that cannot be determined at compile time, to ensure

tests/run-coverage/dead_code.rs

@@ -1,4 +1,4 @@
-#![allow(unused_assignments, unused_variables)]
+#![allow(dead_code, unused_assignments, unused_variables)]
 
 pub fn unused_pub_fn_not_in_library() {
     // Initialize test constants in a way that cannot be determined at compile time, to ensure

tests/run-coverage/issue-93054.coverage

@@ -1,3 +1,5 @@
+   LL|       |#![allow(dead_code, unreachable_code)]
+   LL|       |
    LL|       |// Regression test for #93054: Functions using uninhabited types often only have a single,
    LL|       |// unreachable basic block which doesn't get instrumented. This should not cause llvm-cov to fail.
    LL|       |// Since these kinds functions can't be invoked anyway, it's ok to not have coverage data for them.