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.

llvm-svn: 94526