Rollup merge of #105354 - BlackHoleFox:apple-deployment-printer, r=oli-obk

Add deployment-target --print flag for Apple targets

This is very useful for crates that need to know what the Apple OS deployment target is for their build scripts or inside of a build environment. Right now, the defaults just get copy/pasted around the ecosystem since they've been stable for so long. But with #104385 in progress, that won't be true anymore and everything will need to move. Ideally whenever it happens again, this could be less painful as everything can ask the compiler what its default is instead.

To show examples of the copy/paste proliferation, here's some crates and/or apps that do:
- [cc](https://github.com/rust-lang/cc-rs/pull/708/files), Soon
-  [mac-notification-sys](https://github.com/h4llow3En/mac-notification-sys/pull/46/files#diff-d0d98998092552a1d3259338c2c71e118a5b8343dd4703c0c7f552ada7f9cb42R10-R12)
- [PyO3](ccb02d1aa1/src/target.rs (L755-L758))
- [Anki](613b5c1034/build/runner/src/bundle/artifacts.rs (L49-L54))
- [jsc-rs](3776726756/xtask/src/build.rs (L402-L405))
... and probably more that a simple GitHub codesearch didn't see

compiler/rustc_session/src/config.rs

@@ -599,6 +599,7 @@ pub enum PrintRequest {
     StackProtectorStrategies,
     LinkArgs,
     SplitDebuginfo,
+    DeploymentTarget,
 }
 
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
@@ -1481,7 +1482,7 @@ pub fn rustc_short_optgroups() -> Vec<RustcOptGroup> {
             "[crate-name|file-names|sysroot|target-libdir|cfg|calling-conventions|\
              target-list|target-cpus|target-features|relocation-models|code-models|\
              tls-models|target-spec-json|all-target-specs-json|native-static-libs|\
-             stack-protector-strategies|link-args]",
+             stack-protector-strategies|link-args|deployment-target]",
         ),
         opt::flagmulti_s("g", "", "Equivalent to -C debuginfo=2"),
         opt::flagmulti_s("O", "", "Equivalent to -C opt-level=2"),
@@ -1931,6 +1932,7 @@ fn collect_print_requests(
         ("all-target-specs-json", PrintRequest::AllTargetSpecs),
         ("link-args", PrintRequest::LinkArgs),
         ("split-debuginfo", PrintRequest::SplitDebuginfo),
+        ("deployment-target", PrintRequest::DeploymentTarget),
     ];
 
     prints.extend(matches.opt_strs("print").into_iter().map(|req| {