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: rust-lang/rust#116973

Author: matthiaskrgr