[ELF] --export-dynamic: don't create dynamic sections for non-PIC static links

The CloudABI (removed from Clang Driver) change from
https://reviews.llvm.org/D29982 does not make sense. GNU ld and gold
don't create dynamic sections for a non-PIC static link when
--export-dynamic is specified.

Creating dynamic sections is harmful in this scenario because we would
consider undefined weak symbols preemptible and generate GLOB_DAT
relocations, breaking the expectation that non-PIC static links only
contain IRELATIVE relocations.

In addition, there are other options that export symbols
(--export-dynamic-symbol, --dynamic-list, etc). It does not make sense
to special case --export-dynamic.