ld: don't attempt to build dynamic sections unnecessarily
This prevents ld from generating zeroed symtab entries for
sections that aren't going to be generated because dynamic
linkage has been disabled (-d was used or no dynamic libs
were seen). Even though they were not explicitly added by
doelf, the section creation process was making them
reachable again.
The windows head is being disconsidered for this because
apparently it's not taking into account debug['d'].
This makes elflint 0.1% happier.
R=golang-dev, rsc, gustavo
CC=golang-dev
https://golang.org/cl/
4638050