Previously objcopy (elfcopy) --add-sections inserted new sections before
.shstrtab, but omitted them if there was no .shstrtab.
Now, after processing existing sections add new sections if they were
not yet added.
PR: 241437
Reported by: arrowd
Submitted by: Tiger Gao <tig@FreeBSDFoundation.org>
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D23571