indicates that an MCSymbol is external or not. (It's true if it's external.)
This will be used to specify the correct information to add to non-lazy
pointers. That will be explained further when this bit is used.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@98199 91177308-0d34-0410-b5e6-96231b3b80d8