Auto merge of #77729 - petrochenkov:mergetarg, r=Mark-Simulacrum

rustc_target: Move some target options from `Target` to `TargetOptions`

The only reason for `Target` to `TargetOptions` to be separate structures is that options in `TargetOptions` have reasonable defaults and options in `Target` don't.
(Otherwise all the options logically belong to a single `Target` struct.)

This PR moves a number of options with reasonable defaults from `Target` to `TargetOptions`, so they no longer needs to be specified explicitly for majority of the targets.
The move also allows to inherit the options from `rustc_target/src/spec/*_base.rs` files in a nicer way.
I didn't change any specific option values here.

The moved options are `target_c_int_width` (defaults to `"32"`), `target_endian` (defaults to `"little"`), `target_os` (defaults to `"none"`), `target_env` (defaults to `""`), `target_vendor` (defaults to `"unknown"`) and `linker_flavor` (defaults to `LinkerFlavor::Gcc`).

Next steps (in later PRs):
- Find a way to merge `TargetOptions` into `Target`
- If not, always access `TargetOptions` fields through `Deref` making it a part of `Target` at least logically (`session.target.target.options.foo` -> `session.target.target.foo`)
- ~Eliminate `session::config::Config` and use `Target` instead (`session.target.target.foo` -> `session.target.foo`)~ Done in #77943.
- Avoid tautologies in option names (`target.target_os` -> `target.os`)
- Resolve _ #77730 (rustc_target: The differences between `target_os = "none"` and `target_os = "unknown"`, and `target_vendor = "unknown"` and `target_vendor = ""` are unclear) noticed during implementation of this PR.

Author: bors

compiler/rustc_target/src/spec/aarch64_apple_darwin.rs

@@ -1,7 +1,7 @@
 use crate::spec::{LinkerFlavor, Target, TargetOptions};
 
 pub fn target() -> Target {
-    let mut base = super::apple_base::opts();
+    let mut base = super::apple_base::opts("macos");
     base.cpu = "apple-a12".to_string();
     base.max_atomic_width = Some(128);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-arch".to_string(), "arm64".to_string()]);
@@ -16,15 +16,9 @@ pub fn target() -> Target {
 
     Target {
         llvm_target,
-        target_endian: "little".to_string(),
         pointer_width: 64,
-        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".to_string(),
         arch: arch.to_string(),
-        target_os: "macos".to_string(),
-        target_env: String::new(),
-        target_vendor: "apple".to_string(),
-        linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions { target_mcount: "\u{1}mcount".to_string(), ..base },
     }
 }

compiler/rustc_target/src/spec/aarch64_apple_ios.rs

@@ -1,19 +1,13 @@
 use super::apple_sdk_base::{opts, Arch};
-use crate::spec::{LinkerFlavor, Target, TargetOptions};
+use crate::spec::{Target, TargetOptions};
 
 pub fn target() -> Target {
-    let base = opts(Arch::Arm64);
+    let base = opts("ios", Arch::Arm64);
     Target {
         llvm_target: "arm64-apple-ios".to_string(),
-        target_endian: "little".to_string(),
         pointer_width: 64,
-        target_c_int_width: "32".to_string(),
         data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".to_string(),
         arch: "aarch64".to_string(),
-        target_os: "ios".to_string(),
-        target_env: String::new(),
-        target_vendor: "apple".to_string(),
-        linker_flavor: LinkerFlavor::Gcc,
         options: TargetOptions {
             features: "+neon,+fp-armv8,+apple-a7".to_string(),
             eliminate_frame_pointer: false,