MachO: rename _outputFileType to avoid shadowing parent field.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@211367 91177308-0d34-0410-b5e6-96231b3b80d8
PE/COFF: move PAGE_SIZE into the PECOFFLinkingContext.

A refactoring, with the added benefit of helping OS X builds.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@211371 91177308-0d34-0410-b5e6-96231b3b80d8