[RemoteMirrors] Clear the Demangler on each iteration of the loop in getFieldTypeInfo. Otherwise the Demangler can end up allocating hundreds of megabytes of memory.

rdar://problem/40826018

Author: mikeash

stdlib/public/Reflection/TypeRefBuilder.cpp

@@ -160,6 +160,7 @@ TypeRefBuilder::getFieldTypeInfo(const TypeRef *TR) {
       auto CandidateMangledName = FD.getMangledTypeName(TypeRefOffset);
       auto NormalizedName = normalizeReflectionName(Dem, CandidateMangledName);
       FieldTypeInfoCache[NormalizedName] = {&FD, &Info};
+      Dem.clear();
     }
   }