[llvm-dlltool] Respect NONAME keyword

[thrimbor]

Summary

This adds proper handling of the NONAME-keyword, which makes llvm-dlltool generate an import using the ordinal instead of the name.
Actual change done by Jannik Vogel, test added by me.

llvm/lib/Object/COFFImportFile.cpp

       ImportType = IMPORT_CONST;
 
     StringRef SymbolName = E.SymbolName.empty() ? E.Name : E.SymbolName;
-    ImportNameType NameType = getNameType(SymbolName, E.Name, Machine, MinGW);
+    ImportNameType NameType = E.Noname
+                                  ? IMPORT_ORDINAL
+                                  : getNameType(SymbolName, E.Name,
+                                                Machine, MinGW);
     Expected<std::string> Name = E.ExtName.empty()
                                      ? SymbolName
                                      : replace(SymbolName, E.Name, E.ExtName);

llvm/test/tools/llvm-dlltool/coff-noname.def

+; RUN: llvm-dlltool -k -m i386 --input-def %s --output-lib %t.a
+; RUN: llvm-readobj %t.a | FileCheck %s
+
+LIBRARY test.dll
+EXPORTS
+ByOrdinalFunction @ 1 NONAME
+ByNameFunction
+
+; CHECK: Name type: ordinal
+; CHECK: Symbol: __imp__ByOrdinalFunction
+; CHECK: Symbol: _ByOrdinalFunction
+; CHECK: Name type: noprefix
+; CHECK: Symbol: __imp__ByNameFunction
+; CHECK: Symbol: _ByNameFunction