Auto merge of #155223 - teor2345:fndef-refactor, r=mati865

Refactor FnDecl and FnSig non-type fields into a new wrapper type





#### Why this Refactor?

This PR is part of an initial cleanup for the [arg splat experiment](https://github.com/rust-lang/rust/issues/153629), but it's a useful refactor by itself.

It refactors the non-type fields of `FnDecl`, `FnSig`, and `FnHeader` into a new packed wrapper types, based on this comment in the `splat` experiment PR:
https://github.com/rust-lang/rust/pull/153697#discussion_r3004637413

It also refactors some common `FnSig` creation settings into their own methods. I did this instead of creating a struct with defaults.

#### Relationship to `splat` Experiment

I don't think we can use functional struct updates (`..default()`) to create `FnDecl` and `FnSig`, because we need the bit-packing for the `splat` experiment.

Bit-packing will avoid breaking "type is small" assertions for commonly used types when `splat` is added.
This PR packs these types:
- ExternAbi: enum + `unwind` variants (38) -> 6 bits
- ImplicitSelfKind: enum variants (5) -> 3 bits
- lifetime_elision_allowed, safety, c_variadic: bool -> 1 bit

#### Minor Changes

Fixes some typos, and applies rustfmt to clippy files that got skipped somehow.

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -3,8 +3,7 @@
 use std::{assert_matches, iter, ptr};
 
 use rustc_abi::{
-    Align, BackendRepr, ExternAbi, Float, HasDataLayout, NumScalableVectors, Primitive, Size,
-    WrappingRange,
+    Align, BackendRepr, Float, HasDataLayout, NumScalableVectors, Primitive, Size, WrappingRange,
 };
 use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh, wants_wasm_eh};
 use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
@@ -820,7 +819,7 @@ fn codegen_llvm_intrinsic_call(
             }
             _ => unreachable!(),
         };
-        assert!(!fn_sig.c_variadic);
+        assert!(!fn_sig.c_variadic());
 
         let ret_layout = self.layout_of(fn_sig.output());
         let llreturn_ty = if ret_layout.is_zst() {
@@ -1640,32 +1639,18 @@ fn get_rust_try_fn<'a, 'll, 'tcx>(
     // `unsafe fn(*mut i8) -> ()`
     let try_fn_ty = Ty::new_fn_ptr(
         tcx,
-        ty::Binder::dummy(tcx.mk_fn_sig(
-            [i8p],
-            tcx.types.unit,
-            false,
-            hir::Safety::Unsafe,
-            ExternAbi::Rust,
-        )),
+        ty::Binder::dummy(tcx.mk_fn_sig_rust_abi([i8p], tcx.types.unit, hir::Safety::Unsafe)),
     );
     // `unsafe fn(*mut i8, *mut i8) -> ()`
     let catch_fn_ty = Ty::new_fn_ptr(
         tcx,
-        ty::Binder::dummy(tcx.mk_fn_sig(
-            [i8p, i8p],
-            tcx.types.unit,
-            false,
-            hir::Safety::Unsafe,
-            ExternAbi::Rust,
-        )),
+        ty::Binder::dummy(tcx.mk_fn_sig_rust_abi([i8p, i8p], tcx.types.unit, hir::Safety::Unsafe)),
     );
     // `unsafe fn(unsafe fn(*mut i8) -> (), *mut i8, unsafe fn(*mut i8, *mut i8) -> ()) -> i32`
-    let rust_fn_sig = ty::Binder::dummy(cx.tcx.mk_fn_sig(
+    let rust_fn_sig = ty::Binder::dummy(cx.tcx.mk_fn_sig_rust_abi(
         [try_fn_ty, i8p, catch_fn_ty],
         tcx.types.i32,
-        false,
         hir::Safety::Unsafe,
-        ExternAbi::Rust,
     ));
     let rust_try = gen_fn(cx, "__rust_try", rust_fn_sig, codegen);
     cx.rust_try_fn.set(Some(rust_try));