Update LLVM lib/Demangle 0cc19b564dd3a2b7ce51840d6...3a4c7cc56c07b2db

Ran:

    cp ~/src/llvm-project/llvm/include/llvm/Demangle/*.{h,def} third_party/llvm/include/llvm/Demangle/
    cp ~/src/llvm-project/llvm/lib/Demangle/*.cpp third_party/llvm/lib/Demangle/
    cp ~/src/llvm-project/llvm/LICENSE.TXT third_party/llvm/LICENSE.txt

New:

* Two demangling fixes for non-type template parameters in the
  Microsoft ABI
* Demangling for built-in type transformations in the Itanium ABI
* Demangling rules for C++20 concepts and requires-expressions in
  the Itanium ABI
* Demangle explicitly named object parameters in the Itanium ABI

(...and some minor tweaks.)

third_party/llvm/include/llvm/Demangle/Demangle.h

@@ -32,7 +32,7 @@ enum : int {
 /// Returns a non-NULL pointer to a NUL-terminated C style string
 /// that should be explicitly freed, if successful. Otherwise, may return
 /// nullptr if mangled_name is not a valid mangling or is nullptr.
-char *itaniumDemangle(std::string_view mangled_name);
+char *itaniumDemangle(std::string_view mangled_name, bool ParseParams = true);
 
 enum MSDemangleFlags {
   MSDF_None = 0,
@@ -67,7 +67,9 @@ char *dlangDemangle(std::string_view MangledName);
 /// demangling occurred.
 std::string demangle(std::string_view MangledName);
 
-bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result);
+bool nonMicrosoftDemangle(std::string_view MangledName, std::string &Result,
+                          bool CanHaveLeadingDot = true,
+                          bool ParseParams = true);
 
 /// "Partial" demangler. This supports demangling a string into an AST
 /// (typically an intermediate stage in itaniumDemangle) and querying certain
@@ -102,7 +104,7 @@ struct ItaniumPartialDemangler {
   char *getFunctionParameters(char *Buf, size_t *N) const;
   char *getFunctionReturnType(char *Buf, size_t *N) const;
 
-  /// If this function has any any cv or reference qualifiers. These imply that
+  /// If this function has any cv or reference qualifiers. These imply that
   /// the function is a non-static member function.
   bool hasFunctionQualifiers() const;
 

third_party/llvm/include/llvm/Demangle/DemangleConfig.h

@@ -86,6 +86,11 @@
 #define DEMANGLE_FALLTHROUGH
 #endif
 
+#ifndef DEMANGLE_ASSERT
+#include <cassert>
+#define DEMANGLE_ASSERT(__expr, __msg) assert((__expr) && (__msg))
+#endif
+
 #define DEMANGLE_NAMESPACE_BEGIN namespace llvm { namespace itanium_demangle {
 #define DEMANGLE_NAMESPACE_END } }