Bitcode: add an auto-upgrade for LTO section name

The bitcode reader looks specifically for `__DATA, __objc_catlist` as a
section name.  However, SVN r304661 removed the spaces (the two names
are functionally equivalent but do not compare equally
lexicographically).  This causes compatibility issues.  Add an
auto-upgrade path for removing the spaces as well as use the new name in
the LTO plugin.

llvm-svn: 315086