Account for LSB on c64 e_entry in the same way as Thumb

Account for LSB on c64 e_entry in the same way as Thumb

The handling is done by putting the value that we want in a buffer and
using that as the entry_symbol.name which lang_end picks up.

Another option would be to find the entry symbol *after* lang_end has
finished (e.g. in elfNN_aarch64_init_file_header) and add the LSB to it
if that symbol is a C64 symbol.

This approach was mainly chosen in order to match more closely what
Thumb has done.

N.b. we set the LSB based on the LSB of the entry point symbol.
If the entry point symbol is in c64 code but is not an STT_FUNC (e.g.
it is an STT_NOTYPE) then the LSB will not be set.
This matches Morello clang behaviour.