Rollup merge of #130777 - azhogin:azhogin/reg-struct-return, r=workingjubilee

rust_for_linux: -Zreg-struct-return commandline flag for X86 (#116973)

Command line flag `-Zreg-struct-return` for X86 (32-bit) for rust-for-linux.
This flag enables the same behavior as the `abi_return_struct_as_int` target spec key.

- Tracking issue: https://github.com/rust-lang/rust/issues/116973

compiler/rustc_interface/src/tests.rs

@@ -832,6 +832,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(precise_enum_drop_elaboration, false);
     tracked!(profile_sample_use, Some(PathBuf::from("abc")));
     tracked!(profiler_runtime, "abc".to_string());
+    tracked!(reg_struct_return, true);
     tracked!(regparm, Some(3));
     tracked!(relax_elf_relocations, Some(true));
     tracked!(remap_cwd_prefix, Some(PathBuf::from("abc")));