Disable debug_asserts inside std due to poor UX (rust-lang#1791)

This is a possible workaround for now to improve the UX around UB
detection in intrinsics when using the MIR Linker. The issue is tracked
here:
model-checking/kani#1740

Basically, the rust toolchain uses a release build that removes all
debug assertions from the standard library. When we switched to using
our custom build of the `std` we decided to enable the debug assertions
in order to catch more potential UBs. However, the UX is not always
great. The assertions don't have any clear descriptions and they may
fail in unexpected places. E.g.: The violation of an intrinsic safety
condition triggers the following failures:
```
> Failed checks: Called `Option::unwrap()` on a `None` value
```

Author: celinval

tests/expected/intrinsics/copy-nonoverlapping/copy-overflow/main.rs

@@ -1,14 +1,7 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
-// kani-flags: --legacy-linker
 //! Checks that `copy_nonoverlapping` triggers an overflow failure if the `count`
 //! argument can overflow a `usize`
-//!
-//! When enabling "--mir-linker", the error we currently get is:
-//! > Failed checks: Called `Option::unwrap()` on a `None` value
-//! This happens because of std debug checks. The `is_nonoverlapping` check has a
-//! `checked_mul().unwrap()` that fails in the overflow scenario.
-//! See <https://github.com/model-checking/kani/issues/1740> for more details.
 #[kani::proof]
 fn test_copy_nonoverlapping_unaligned() {
     let arr: [i32; 3] = [0, 1, 0];

tests/expected/intrinsics/copy-nonoverlapping/copy-unaligned-dst/main.rs

@@ -1,9 +1,6 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-// kani-flags: --legacy-linker
-//! The MIR linker errors are not quite user friendly. For more details, see
-//! <https://github.com/model-checking/kani/issues/1740>
 //! Checks that `copy_nonoverlapping` fails when `dst` is not aligned.
 
 #[kani::proof]

tests/expected/intrinsics/copy-nonoverlapping/copy-unaligned-src/main.rs

@@ -1,9 +1,6 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-// kani-flags: --legacy-linker
-//! The MIR linker errors are not quite user friendly. For more details, see
-//! <https://github.com/model-checking/kani/issues/1740>
 //! Checks that `copy_nonoverlapping` fails when `src` is not aligned.
 #[kani::proof]
 fn test_copy_nonoverlapping_unaligned() {

tests/expected/intrinsics/copy/copy-unaligned-dst/main.rs

@@ -1,9 +1,6 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-// kani-flags: --legacy-linker
-//! The MIR linker errors are not quite user friendly. For more details, see
-//! <https://github.com/model-checking/kani/issues/1740>
 //! Checks that `copy` fails when `dst` is not aligned.
 #[kani::proof]
 fn test_copy_unaligned() {

tests/expected/intrinsics/copy/copy-unaligned-src/main.rs

@@ -1,9 +1,6 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-// kani-flags: --legacy-linker
-//! The MIR linker errors are not quite user friendly. For more details, see
-//! <https://github.com/model-checking/kani/issues/1740>
 //! Checks that `copy` fails when `src` is not aligned.
 #[kani::proof]
 fn test_copy_unaligned() {

tests/expected/intrinsics/write_bytes/unaligned/main.rs

@@ -1,9 +1,6 @@
 // Copyright Kani Contributors
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
-// kani-flags: --legacy-linker
-//! The MIR linker errors are not quite user friendly. For more details, see
-//! <https://github.com/model-checking/kani/issues/1740>
 //! Checks that `write_bytes` fails when `dst` is not aligned.
 //! This test is a modified version of the example in
 //! https://doc.rust-lang.org/std/ptr/fn.write_bytes.html

tools/build-kani/src/sysroot.rs

@@ -93,6 +93,10 @@ pub fn build_lib() {
         "dev",
         "--config",
         "profile.dev.panic=\"abort\"",
+        // Disable debug assertions for now as a mitigation for
+        // https://github.com/model-checking/kani/issues/1740
+        "--config",
+        "profile.dev.debug-assertions=false",
         "--config",
         "host.rustflags=[\"--cfg=kani\"]",
         "--target",
@@ -126,7 +130,6 @@ pub fn build_lib() {
     cp_files(&kani_rlib_folder, &sysroot_lib, &is_rlib).unwrap();
 
     // Copy `std` libraries and dependencies to sysroot folder following expected path format.
-    // TODO: Create a macro for all these push.
     let src_path = path_buf!(target_folder, target, "debug", "deps");
 
     let dst_path = path_buf!(sysroot_lib, "rustlib", target, "lib");