It's useful to be able to get information about classes without a
running process, ie. when debugging a coredump.

These flags were removed in d426343418aab6148706860bd1678ac309dc12c0 and
print_flags is broken because of it.

Tested and it works with both AR and ST tables, with live process and
core dumps.

Useful for core dumps. It used to not work because:

    (gdb) p !""
    evaluation of this expression requires the target program to be active
    (gdb) p 0 == ""
    evaluation of this expression requires the target program to be active

When doing out-of-source builds I often end up wanting to use gdb from
inside a build directory.

Currently if I do that the `.gdbinit` in the ruby source directory is
not read.

Attempting to manually load the `.gdbinit` from the Ruby source
directory errors because of hard coded file-paths that assume we're
running gdb from inside the source tree.

Adding the `-s` flag to the `source` command when loading relative files
signals to gdb to search in the source search path for the required
file, rather than just the current directory.

This allows me to use a custom `.gdbinit` from my build directory that
sets the correct source directory and then loads the Ruby `.gdbinit`.

```
dir ../src
source ../src/.gdbinit
```