Rollup merge of #77415 - ecstatic-morse:const-checking-async-block, r=oli-obk

Better error message for `async` blocks in a const-context

Improves the error message for the case in #77361.

r? @oli-obk

src/test/ui/consts/async-block.rs

@@ -0,0 +1,8 @@
+// From <https://github.com/rust-lang/rust/issues/77361>
+
+// edition:2018
+
+const _: i32 = { core::mem::ManuallyDrop::new(async { 0 }); 4 };
+//~^ `async` block
+
+fn main() {}

src/test/ui/consts/async-block.stderr

@@ -0,0 +1,8 @@
+error: `async` blocks are not allowed in constants
+  --> $DIR/async-block.rs:5:47
+   |
+LL | const _: i32 = { core::mem::ManuallyDrop::new(async { 0 }); 4 };
+   |                                               ^^^^^^^^^^^
+
+error: aborting due to previous error
+