[lldb] Use mangled symbol name to look for __asan::AsanDie()

After aed965d5 we no longer demangle full symbol names while indexing the
symbol table which means we have to use the mangled name instead of the
demangled name to find the symbol for __asan::AsanDie().

This fixes the following two tests:

  lldb-api :: functionalities/asan/TestMemoryHistory.py
  lldb-api :: functionalities/asan/TestReportData.py