Revert "Centralize the information about which object format we are using."

This reverts commit r245047.

It was failing on the darwin bots. The problem was that when running

./bin/llc -march=msp430

llc gets to

  if (TheTriple.getTriple().empty())
    TheTriple.setTriple(sys::getDefaultTargetTriple());

Which means that we go with an arch of msp430 but a triple of
x86_64-apple-darwin14.4.0 which fails badly.

That code has to be updated to select a triple based on the value of
march, but that is not a trivial fix.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245062 91177308-0d34-0410-b5e6-96231b3b80d8