[PECOFF] Fix .bss section alignment

Previously the alignment of the .bss section was not
properly set because of a bug in AtomizeDefinedSymbolsInSection.
We set the alignment of the section at the end of the function,
but we use an eraly return for the .bss section, so the code had
been skipped.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@212571 91177308-0d34-0410-b5e6-96231b3b80d8