dsymutil: Re-add missing -latomic (#85380)

This was accidentally removed in
https://reviews.llvm.org/D137799#4657404 /
https://reviews.llvm.org/D137799#C3933303OL44, and downstream projects
are forced to add it back. For example,
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=4e26331a5ee87928a16888c36d51e270f0f10f90



Fix this, by re-adding it.

Co-authored-by: MarcoFalke <*~=`'#}+{/-|&amp;$^_@721217.xyz>