Set the minimum deployment target for aarch64-apple-watchos

To match what's done in LLVM 21.

compiler/rustc_target/src/spec/base/apple/mod.rs

@@ -304,7 +304,7 @@ impl OSVersion {
     /// to raise the minimum OS version.
     ///
     /// This matches what LLVM does, see in part:
-    /// <https://github.com/llvm/llvm-project/blob/llvmorg-18.1.8/llvm/lib/TargetParser/Triple.cpp#L1900-L1932>
+    /// <https://github.com/llvm/llvm-project/blob/llvmorg-21.1.3/llvm/lib/TargetParser/Triple.cpp#L2140-L2175>
     pub fn minimum_deployment_target(target: &Target) -> Self {
         let (major, minor, patch) = match (&*target.os, &*target.arch, &*target.env) {
             ("macos", "aarch64", _) => (11, 0, 0),
@@ -315,6 +315,9 @@ impl OSVersion {
             ("ios", _, "macabi") => (13, 1, 0),
             ("tvos", "aarch64", "sim") => (14, 0, 0),
             ("watchos", "aarch64", "sim") => (7, 0, 0),
+            // True Aarch64 on watchOS (instead of their Aarch64 Ilp32 called `arm64_32`) has been
+            // available since Xcode 14, but it's only actually used more recently in watchOS 26.
+            ("watchos", "aarch64", "") if !target.llvm_target.starts_with("arm64_32") => (26, 0, 0),
             (os, _, _) => return Self::os_minimum_deployment_target(os),
         };
         Self { major, minor, patch }

tests/run-make/apple-deployment-target/rmake.rs

@@ -33,6 +33,7 @@ fn main() {
         // armv7s-apple-ios and i386-apple-ios only supports iOS 10.0
         "ios" if target() == "armv7s-apple-ios" || target() == "i386-apple-ios" => ("10.0", "10.0"),
         "ios" => ("15.0", "16.0"),
+        "watchos" if target() == "aarch64-apple-watchos" => ("28.0", "30.0"),
         "watchos" => ("7.0", "9.0"),
         "tvos" => ("14.0", "15.0"),
         "visionos" => ("1.1", "1.2"),