readelf: More sanity checks before trying to display interpreter string.

Check there is a SHT_PROGBITS section at the offset given by p_offsets for
a PT_INTERP segment before trying to display the interpreter string.

Signed-off-by: Mark Wielaard <mjw@redhat.com>
libdwfl: elf-from-memory.c (elf_from_remote_memory): Check against p64 p_type.

There was a type in the case of parsing ELFCLASS64 phdrs. Check against
p64 p_type, not the p32 p_type which at a different location in the union.

Signed-off-by: Mark Wielaard <mjw@redhat.com>