Rollup merge of rust-lang#132417 - madsmtm:document-darwin-macos-diff…

…erence, r=jieyouxu

macOS: Document the difference between Clang's `-darwin` and `-macosx` targets

`rustc`'s `*-apple-darwin` targets are badly named (they should've been called `*-apple-macos`), and this causes confusion wrt. the similarly named but somewhat incompatible Clang targets.

So let's document the difference to at least make things a _little_ easier on our users.

`@rustbot` label O-macos  A-docs

src/doc/rustc/src/platform-support/apple-darwin.md

@@ -52,5 +52,10 @@ Cross-compilation of these targets are supported using Clang, but may require
 Xcode or the macOS SDK (`MacOSX.sdk`) to be available to compile C code and
 to link.
 
+The Clang target is suffixed with `-macosx`. Clang's `-darwin` target refers
+to Darwin platforms in general (macOS/iOS/tvOS/watchOS/visionOS), and requires
+the `-mmacosx-version-min=...`, `-miphoneos-version-min=...` or similar flags
+to disambiguate.
+
 The path to the SDK can be passed to `rustc` using the common `SDKROOT`
 environment variable.