Allow Sparc back-end to take the address of a function (or other global object)

[lero_chris]

Summary

The following code would not work before this patch, due to the inability to take the address of a global object:

void func1() {

...

}

int main(int argc, char** argv) {

void (*pFunc)();
pFunc = &func1
pFunc();
...

}

[jacob_hansen]

This looks good for me (not sure I can formally accept it as I do not yet have SVN write access though).

[lero_chris]

Unit tests to go with this change.

DelaySlotFiller.cpp

void Filler::insertCallDefsUses(MachineBasicBlock::iterator MI,
   case SP::CALLri:
     assert(MI->getNumOperands() >= 2);
     const MachineOperand &Reg = MI->getOperand(0);
     assert(Reg.isReg() && "CALL first operand is not a register.");
     assert(Reg.isUse() && "CALL first operand is not a use.");
     RegUses.insert(Reg.getReg());
 
     const MachineOperand &RegOrImm = MI->getOperand(1);
-    if (RegOrImm.isImm())
+    if (RegOrImm.isImm() || RegOrImm.isGlobal())
         break;
     assert(RegOrImm.isReg() && "CALLrr second operand is not a register.");
     assert(RegOrImm.isUse() && "CALLrr second operand is not a use.");
     RegUses.insert(RegOrImm.getReg());
     break;
   }
 }