Remove Linkage::Appending

It can only be used for certain LLVM internal variables like
llvm.global_ctors which users are not allowed to define.

Author: bjorn3

src/base.rs

@@ -49,7 +49,6 @@ pub fn global_linkage_to_gcc(linkage: Linkage) -> GlobalKind {
         Linkage::LinkOnceODR => unimplemented!(),
         Linkage::WeakAny => unimplemented!(),
         Linkage::WeakODR => unimplemented!(),
-        Linkage::Appending => unimplemented!(),
         Linkage::Internal => GlobalKind::Internal,
         Linkage::ExternalWeak => GlobalKind::Imported, // TODO(antoyo): should be weak linkage.
         Linkage::Common => unimplemented!(),
@@ -65,7 +64,6 @@ pub fn linkage_to_gcc(linkage: Linkage) -> FunctionType {
         Linkage::LinkOnceODR => unimplemented!(),
         Linkage::WeakAny => FunctionType::Exported, // FIXME(antoyo): should be similar to linkonce.
         Linkage::WeakODR => unimplemented!(),
-        Linkage::Appending => unimplemented!(),
         Linkage::Internal => FunctionType::Internal,
         Linkage::ExternalWeak => unimplemented!(),
         Linkage::Common => unimplemented!(),