Replace large swaths of copy-n-paste code with obvious helper function...

Replace large swaths of copy-n-paste code with obvious helper function...
 - Which was already present in the module!

 - I skipped this xform for Alpha, since it runs an extra pass during assembly
   emission, but not when emitting assembly via the DumpAsm flag.

 - No functionality change.

--
ddunbar@giles:llvm$ svn diff | grep '^- ' | sort | uniq -c
  18 -      PM.add(AsmPrinterCtor(ferrs(), *this, true));
  18 -    assert(AsmPrinterCtor && "AsmPrinter was not linked in");
  18 -    if (AsmPrinterCtor)
  18 -  if (DumpAsm) {
  18 -  }
ddunbar@giles:llvm$ svn diff | grep '^+ ' | sort | uniq -c
  18 +    addAssemblyEmitter(PM, OptLevel, true, ferrs());
  18 +  if (DumpAsm)
--

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75782 91177308-0d34-0410-b5e6-96231b3b80d8