[PECOFF] Set section name for BSS atoms.
[PECOFF] Set section name for BSS atoms.

This change has no effect now, but will be needed to emit BSS atoms
to .bss section.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@193556 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld