[llvm][Demangle] Sync with libcxxabi

[Michael137]

Will sync in same patch as libcxxabi

llvm/include/llvm/Demangle/ItaniumDemangle.h

 #include <algorithm>
 #include <cassert>
 #include <cctype>
 #include <cstdio>
 #include <cstdlib>
 #include <cstring>
 #include <limits>
 #include <new>
-#include <type_traits>
 #include <utility>
 
 DEMANGLE_NAMESPACE_BEGIN
 
 template <class T, size_t N> class PODSmallVector {
-  static_assert(std::is_trivial_v<T>, "T is required to be a trivial type");
+  static_assert(std::is_pod<T>::value,
+                "T is required to be a plain old data type");
 
   T *First = nullptr;
   T *Last = nullptr;
   T *Cap = nullptr;
-  T Inline[N] = {};
+  T Inline[N] = {0};
 
   bool isInline() const { return First == Inline; }
 
   void clearInline() {
     First = Inline;
     Last = Inline;
     Cap = Inline + N;
   }
struct AbiTagAttr : Node {
 
   AbiTagAttr(Node* Base_, StringView Tag_)
       : Node(KAbiTagAttr, Base_->RHSComponentCache,
              Base_->ArrayCache, Base_->FunctionCache),
         Base(Base_), Tag(Tag_) {}
 
   template<typename Fn> void match(Fn F) const { F(Base, Tag); }
 
+  StringView getBaseName() const override { return Base->getBaseName(); }
+
   void printLeft(OutputBuffer &OB) const override {
     Base->printLeft(OB);
     OB += "[abi:";
     OB += Tag;
     OB += "]";
   }
 };