visionOS: Update deployment-target flag for Xcode 15.1 beta

Use the same flags Xcode adds for `XROS_DEPLOYMENT_TARGET`.  They are
`-target arm64-apple-xros1.0` and `-target arm64-apple-xros1.0-simulator`,
where `1.0` is the deployment target version.

Fixes: #25188

Modules/Platform/Apple-Clang.cmake

@@ -26,10 +26,10 @@ macro(__apple_compiler_clang lang)
     set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mtvos-version-min=")
   elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/AppleTVSimulator")
     set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mtvos-simulator-version-min=")
-    elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/XROS")
-    set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mtargetos=xros")
+  elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/XROS")
+    set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "--target=<ARCH>-apple-xros<VERSION_MIN>")
   elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/XRSimulator")
-    set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mtargetos=xros")
+    set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "--target=<ARCH>-apple-xros<VERSION_MIN>-simulator")
   elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/WatchOS")
     set(CMAKE_${lang}_OSX_DEPLOYMENT_TARGET_FLAG "-mwatchos-version-min=")
   elseif(_CMAKE_OSX_SYSROOT_PATH MATCHES "/WatchSimulator")

Source/cmLocalGenerator.cxx

@@ -1983,10 +1983,43 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
         "CMAKE_" + lang + "_OSX_DEPLOYMENT_TARGET_FLAG";
       cmValue deploymentTargetFlag =
         this->Makefile->GetDefinition(deploymentTargetFlagVar);
-      if (cmNonempty(deploymentTargetFlag)) {
+      if (cmNonempty(deploymentTargetFlag) &&
+          // CMAKE_<LANG>_COMPILER_TARGET overrides a --target= for
+          // CMAKE_OSX_DEPLOYMENT_TARGET, e.g., for visionOS.
+          (!cmHasLiteralPrefix(*deploymentTarget, "--target=") ||
+           this->Makefile
+             ->GetDefinition(cmStrCat("CMAKE_", lang, "_COMPILER_TARGET"))
+             .IsEmpty())) {
+        std::string flag = *deploymentTargetFlag;
+
+        // Add the deployment target architecture to the flag, if needed.
+        static const std::string kARCH = "<ARCH>";
+        std::string::size_type archPos = flag.find(kARCH);
+        if (archPos != std::string::npos) {
+          // This placeholder is meant for visionOS, so default to arm64
+          // unless only non-arm64 archs are given.
+          std::string const arch =
+            (archs.empty() || cm::contains(archs, "arm64")) ? "arm64"
+                                                            : archs[0];
+          // Replace the placeholder with its value.
+          flag = cmStrCat(flag.substr(0, archPos), arch,
+                          flag.substr(archPos + kARCH.size()));
+        }
+
+        // Add the deployment target version to the flag.
+        static const std::string kVERSION_MIN = "<VERSION_MIN>";
+        std::string::size_type verPos = flag.find(kVERSION_MIN);
+        if (verPos != std::string::npos) {
+          // Replace the placeholder with its value.
+          flag = cmStrCat(flag.substr(0, verPos), *deploymentTarget,
+                          flag.substr(verPos + kVERSION_MIN.size()));
+        } else {
+          // There is no placeholder, so append the value.
+          flag = cmStrCat(flag, *deploymentTarget);
+        }
+
         flags += " ";
-        flags += *deploymentTargetFlag;
-        flags += *deploymentTarget;
+        flags += flag;
       }
     }
   }