rust_for_linux: -Zregparm=<N> commandline flag for X86 (#116972)

compiler/rustc_middle/src/ty/layout.rs

@@ -21,7 +21,9 @@ use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span};
 use rustc_target::abi::call::FnAbi;
 use rustc_target::abi::{FieldIdx, TyAbiInterface, VariantIdx, call};
 use rustc_target::spec::abi::Abi as SpecAbi;
-use rustc_target::spec::{HasTargetSpec, HasWasmCAbiOpt, PanicStrategy, Target, WasmCAbi};
+use rustc_target::spec::{
+    HasTargetSpec, HasWasmCAbiOpt, HasX86AbiOpt, PanicStrategy, Target, WasmCAbi, X86Abi,
+};
 use tracing::debug;
 use {rustc_abi as abi, rustc_hir as hir};
 
@@ -544,6 +546,12 @@ impl<'tcx> HasWasmCAbiOpt for TyCtxt<'tcx> {
     }
 }
 
+impl<'tcx> HasX86AbiOpt for TyCtxt<'tcx> {
+    fn x86_abi_opt(&self) -> X86Abi {
+        X86Abi { regparm: self.sess.opts.unstable_opts.regparm }
+    }
+}
+
 impl<'tcx> HasTyCtxt<'tcx> for TyCtxt<'tcx> {
     #[inline]
     fn tcx(&self) -> TyCtxt<'tcx> {
@@ -595,6 +603,12 @@ impl<'tcx> HasWasmCAbiOpt for LayoutCx<'tcx> {
     }
 }
 
+impl<'tcx> HasX86AbiOpt for LayoutCx<'tcx> {
+    fn x86_abi_opt(&self) -> X86Abi {
+        self.calc.cx.x86_abi_opt()
+    }
+}
+
 impl<'tcx> HasTyCtxt<'tcx> for LayoutCx<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx> {
         self.calc.cx