[gn build] Fix link with ld.bfd and gold.

lld's symbol resolution algorithm makes it not depend on
the order of object files and libraries, but ld.bfd and
gold require listing dependencies later on the link line.
Put {{libs}} after {{inputs}} so that e.g. -lpthreads
appears after the object files, not before it.

Differential Revision: https://reviews.llvm.org/D81035