[lld] r314616 - Run writeTo() concurrently.

[George Rimar via llvm-commits]

>Author: ruiu
>Date: Sat Sep 30 19:25:34 2017
>New Revision: 314616
>
>URL: http://llvm.org/viewvc/llvm-project?rev=314616&view=rev
>Log:
>Run writeTo() concurrently.
>
>I don't know why we didn't use parallelForEach to call writeTo,
>but there should be no reason to not do that, as most writeTo
>functions are safe to run concurrently.

We already were calling parallelForEachN inside OutputSection::writeTo()
for proccessing input sections. 
Given that I wonder did this commit really speed up things ?
I am asking mostly because of PR34806.

George.