[PATCH] [lld][core] sectionGroup support.

[Rafael Espíndola]

> Yes.  There would need to be another map<> in the symbol table just for
> groups, and the symbol table would
> need to look at the atom’s contentType to see if it goes into the the new
> group map or the existing _nameTable.
> When there is a collision in the group map, all atoms in one group (the new
> one?) need to be added to
> the _replacementAtoms map to be removed.

I might be misunderstanding something, but if I remember correctly one
of the features of how groups is defined on elf is that the linker can
avoid even reading those sections if it already found a group with
that symbol.

We want deterministic output from lld, so we can't just use the first
to be found during a parallel read, but it also seems wasteful to
fully atomize these sections just to discard them.

Cheers,
Rafael