Provide a minimum OS version (11) for ARM/macOS

This gives LLVM enough information to generate a
"platform load-command" in the MachO object file.

Fixes #7941

src/LLVM_Runtime_Linker.cpp

@@ -496,7 +496,10 @@ llvm::Triple get_triple_for_target(const Target &target) {
             triple.setOS(llvm::Triple::Fuchsia);
         } else if (target.os == Target::OSX) {
             triple.setVendor(llvm::Triple::Apple);
-            triple.setOS(llvm::Triple::MacOSX);
+            // Setting a minimum OS version here enables LLVM to include platform
+            // metadata in the MachO object file. Without this, Xcode 15's ld
+            // issues warnings about missing the "platform load command".
+            triple.setOSName("macos11");
             triple.setArchName("arm64");
         } else if (target.os == Target::NoOS) {
             // For bare-metal environments