Re-land [LLD] Remove global state in lldCommon

Move all variables at file-scope or function-static-scope into a hosting structure (lld::CommonLinkerContext) that lives at lldMain()-scope. Drivers will inherit from this structure and add their own global state, in the same way as for the existing COFFLinkerContext.

See discussion in https://lists.llvm.org/pipermail/llvm-dev/2021-June/151184.html

The previous land f860fe36 caused issues in https://lab.llvm.org/buildbot/#/builders/123/builds/8383, fixed by 22ee510d.

Differential Revision: https://reviews.llvm.org/D108850