Add a bit along with the MCSymbols stored in the MachineModuleInfo maps that

Add a bit along with the MCSymbols stored in the MachineModuleInfo maps that
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