[clang] [Clang][AArch64] set default mtune for macOS (PR #179136)

[Jon Roelofs via cfe-commits]

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@@ -13,6 +13,7 @@
 #include "llvm/Option/ArgList.h"
 #include "llvm/TargetParser/AArch64TargetParser.h"
 #include "llvm/TargetParser/Host.h"
+#include <optional>
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jroelofs wrote:

https://llvm.org/docs/CodingStandards.html#include-as-little-as-possible

https://github.com/llvm/llvm-project/pull/179136