Move "Assigned" bit from SectionBase to InputSectionBase.
Move "Assigned" bit from SectionBase to InputSectionBase.

This bit is to manage whether an input section has already been assigned
to some output section by linker scripts or not. So it logically belongs
to InputSectionBase. SectionBase is a common base class for input and
output sections, so that wasn't the right place to define the bit.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@316879 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld