Rollup merge of #126502 - cuviper:dump-mir-exclude-alloc-bytes, r=estebank

Ignore allocation bytes in some mir-opt tests

This adds `rustc -Zdump-mir-exclude-alloc-bytes` to skip writing allocation bytes in MIR dumps, and applies it to tests that were failing on s390x due to its big-endian byte order.

Fixes #126261

compiler/rustc_interface/src/tests.rs

@@ -691,6 +691,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(dump_mir, Some(String::from("abc")));
     untracked!(dump_mir_dataflow, true);
     untracked!(dump_mir_dir, String::from("abc"));
+    untracked!(dump_mir_exclude_alloc_bytes, true);
     untracked!(dump_mir_exclude_pass_number, true);
     untracked!(dump_mir_graphviz, true);
     untracked!(dump_mono_stats, SwitchWithOptPath::Enabled(Some("mono-items-dir/".into())));