[llvm][Demangle][NFC] Sync latest libcxxabi/demangle

[Michael137]

Summary

Changes applied using:

./libcxxabi//src/demangle/cp-to-llvm.sh

[jhenderson]

LGTM.

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;
   }