Support ELF files of unknown type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222208 91177308-0d34-0410-b5e6-96231b3b80d8
Fix covered switch warning

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222209 91177308-0d34-0410-b5e6-96231b3b80d8
Update testing case that was accidently duplicated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222210 91177308-0d34-0410-b5e6-96231b3b80d8
IR: Move MDNode operands from the back to the front

Having the operands at the back prevents subclasses from safely adding
fields.  Move them to the front.

Instead of replicating the custom `malloc()`, `free()` and `DestroyFlag`
logic that was there before, overload `new` and `delete`.

I added calls to a new `GenericMDNode::dropAllReferences()` in
`LLVMContextImpl::~LLVMContextImpl()`.  There's a maze of callbacks
happening during teardown, and this resolves them before we enter
the destructors.

Part of PR21532.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222211 91177308-0d34-0410-b5e6-96231b3b80d8