[libcxxabi] Fix build after D111947

GitOrigin-RevId: 34c97d5ae35405106b7e34763882756a65ff2d67
diff --git a/src/cxa_demangle.cpp b/src/cxa_demangle.cpp
index 3045f6e..6f46a94 100644
--- a/src/cxa_demangle.cpp
+++ b/src/cxa_demangle.cpp
@@ -342,13 +342,13 @@
 
   int InternalStatus = demangle_success;
   Demangler Parser(MangledName, MangledName + std::strlen(MangledName));
-  OutputStream S;
+  OutputBuffer S;
 
   Node *AST = Parser.parse();
 
   if (AST == nullptr)
     InternalStatus = demangle_invalid_mangled_name;
-  else if (!initializeOutputStream(Buf, N, S, 1024))
+  else if (!initializeOutputBuffer(Buf, N, S, 1024))
     InternalStatus = demangle_memory_alloc_failure;
   else {
     assert(Parser.ForwardTemplateRefs.empty());