[llvm] [Docs] Document IIT encoding flow for intrinsic type signatures (PR #185453)

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``````````bash
git-clang-format --diff origin/main HEAD --extensions cpp -- llvm/lib/IR/Intrinsics.cpp llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp --diff_from_common_commit
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``````````diff
diff --git a/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp b/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
index 77175c22f..f9fcbd44b 100644
--- a/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
+++ b/llvm/utils/TableGen/Basic/IntrinsicEmitter.cpp
@@ -336,8 +336,8 @@ static std::optional<uint32_t> encodePacked(const TypeSigTy &TypeSig) {
 
 /// Emit IIT_Table[] and IIT_LongEncodingTable[] into \p OS
 /// (included via GET_INTRINSIC_GENERATOR_GLOBAL in Intrinsics.cpp).
-/// TypeInfoGen<> in Intrinsics.td builds the TypeSig list, 
-/// which IntrinsicEmitter.cpp packs using encodePacked(). 
+/// TypeInfoGen<> in Intrinsics.td builds the TypeSig list,
+/// which IntrinsicEmitter.cpp packs using encodePacked().
 /// Check the MSB of the IIT_Table entry to determine the following:
 ///   Fixed (MSB=0): all IIT codes < 16 and nibble-packed value fits in
 ///     FixedEncodingTy with MSB clear. Stored directly in IIT_Table[].

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https://github.com/llvm/llvm-project/pull/185453