libnixt/serialize: workaround for libcxx .view()

libnixt/include/nixt/SerializeSupport.h

@@ -23,7 +23,18 @@ std::size_t write(std::ostream &OS, const T &Data) {
 class StringTable {
 public:
   std::size_t write(std::string Str);
-  std::string_view view() { return OS.view(); }
+
+  // __WORKAROUND__
+  // libcxx implements .view in recent patch:
+  // https://github.com/llvm/llvm-project/commit/81ad5a5cb87740c62b30a4f8232770bd5eb7fc45
+  // So on macOS this is not available.
+  std::string_view view() {
+#if defined(__GLIBCXX__)
+    return OS.view();
+#else
+    return OS.rdbuf()->view();
+#endif
+  }
 
 private:
   std::map<std::string, std::size_t> Map;