cxxll::java_class: Work around clang name lookup issue

This might be a bug in clang, or the previous code could actually be
invalid C++.  (GCC accepts it.)
database (intern_hash): Avoid C++11 language feature

GCC accepts this reference to a non-static member even in C++98,
but clang does not and is correct to reject this program.
update_elf_closure: Avoid using operator[] on strings

This was a leftover from the const char * -> std::string refactoring.