Move getJTISymbol from MachineJumpTableInfo to MachineFunction,

Move getJTISymbol from MachineJumpTableInfo to MachineFunction,
which is more convenient, and change getPICJumpTableRelocBaseExpr
to take a MachineFunction to match.

Next, move the X86 code that create a PICBase symbol to
X86TargetLowering::getPICBaseSymbol from
X86MCInstLower::GetPICBaseSymbol, which was an asmprinter specific
library.  This eliminates a 'gross hack', and allows us to
implement X86ISelLowering::getPICJumpTableRelocBaseExpr which now
calls it.

This in turn allows us to eliminate the
X86AsmPrinter::printPICJumpTableSetLabel method, which was the
only overload of printPICJumpTableSetLabel.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94526 91177308-0d34-0410-b5e6-96231b3b80d8