[lldb] Make SupportFile's FileSpec and Checksum const (NFC)

Author: JDevlieghere

lldb/include/lldb/Utility/SupportFile.h

@@ -72,8 +72,8 @@ class SupportFile {
   virtual const FileSpec &Materialize() { return m_file_spec; }
 
 protected:
-  FileSpec m_file_spec;
-  Checksum m_checksum;
+  const FileSpec m_file_spec;
+  const Checksum m_checksum;
 };
 
 } // namespace lldb_private