Rollup merge of rust-lang#130777 - azhogin:azhogin/reg-struct-return,…

… r=workingjubilee

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

src/context.rs

@@ -544,7 +544,10 @@ impl<'gcc, 'tcx> HasWasmCAbiOpt for CodegenCx<'gcc, 'tcx> {
 
 impl<'gcc, 'tcx> HasX86AbiOpt for CodegenCx<'gcc, 'tcx> {
     fn x86_abi_opt(&self) -> X86Abi {
-        X86Abi { regparm: self.tcx.sess.opts.unstable_opts.regparm }
+        X86Abi {
+            regparm: self.tcx.sess.opts.unstable_opts.regparm,
+            reg_struct_return: self.tcx.sess.opts.unstable_opts.reg_struct_return,
+        }
     }
 }