Adding dllimport, dllexport and external weak linkage types.
DLL* linkages got full (I hope) codegeneration support in C & both x86
assembler backends.
External weak linkage added for future use, we don't provide any
codegeneration, etc. support for it.

llvm-svn: 30374
diff --git a/llvm/lib/Target/Alpha/AlphaAsmPrinter.cpp b/llvm/lib/Target/Alpha/AlphaAsmPrinter.cpp
index 2ce4865..52e2bb6 100644
--- a/llvm/lib/Target/Alpha/AlphaAsmPrinter.cpp
+++ b/llvm/lib/Target/Alpha/AlphaAsmPrinter.cpp
@@ -258,6 +258,14 @@
         case GlobalValue::GhostLinkage:
           std::cerr << "GhostLinkage cannot appear in AlphaAsmPrinter!\n";
           abort();
+        case GlobalValue::DLLImportLinkage:
+          std::cerr << "DLLImport linkage is not supported by this target!\n";
+          abort();
+        case GlobalValue::DLLExportLinkage:
+          std::cerr << "DLLExport linkage is not supported by this target!\n";
+          abort();
+        default:
+          assert(0 && "Unknown linkage type!");
         }
 
         EmitAlignment(Align);