[clang] [llvm] [ADT] Add and use (for AArch64) `ValueOrSentinel<T, Sentinel>` (PR #158120)

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``````````bash
git-clang-format --diff origin/main HEAD --extensions cpp,h -- llvm/include/llvm/ADT/ValueOrSentinel.h llvm/unittests/ADT/ValueOrSentinelTest.cpp clang/include/clang/Basic/UnsignedOrNone.h llvm/lib/Target/AArch64/AArch64FrameLowering.cpp llvm/lib/Target/AArch64/AArch64ISelLowering.cpp llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h
``````````

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changing `origin/main` to the base branch/commit you want to compare against.
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View the diff from clang-format here.
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``````````diff
diff --git a/llvm/include/llvm/ADT/ValueOrSentinel.h b/llvm/include/llvm/ADT/ValueOrSentinel.h
index 5f4a80f2b..290ef9f0a 100644
--- a/llvm/include/llvm/ADT/ValueOrSentinel.h
+++ b/llvm/include/llvm/ADT/ValueOrSentinel.h
@@ -36,7 +36,7 @@ template <typename T, T Sentinel,
 class ValueOrSentinel {
 public:
   constexpr ValueOrSentinel() = default;
-  constexpr ValueOrSentinel(std::nullopt_t){};
+  constexpr ValueOrSentinel(std::nullopt_t) {};
 
   constexpr ValueOrSentinel(T Value) : Value(Adjust::toRepresentation(Value)) {
     assert(this->Value != Sentinel &&
@@ -76,7 +76,7 @@ public:
   constexpr T toInternalRepresentation() const { return Value; }
 
 protected:
-  ValueOrSentinel(std::nullopt_t, T Value) : Value(Value){};
+  ValueOrSentinel(std::nullopt_t, T Value) : Value(Value) {};
 
   T Value{Sentinel};
 };

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https://github.com/llvm/llvm-project/pull/158120