[llvm-readobj] Support -needed-libs option for COFF files

[phosek]

Summary

This implements the -needed-libs option in the COFF dumper.

[phosek]

Test added.

[rnk]

lgtm

llvm/trunk/test/tools/llvm-readobj/coff-needed-libs.test

+RUN: llvm-readobj -needed-libs %p/Inputs/needed-libs.obj.coff-am64 | FileCheck %s
+
+CHECK:      NeededLibraries [
+CHECK-NEXT:   KERNEL32.dll
+CHECK-NEXT: ]

llvm/trunk/tools/llvm-readobj/COFFDumper.cpp

COFFDumper(const llvm::object::COFFObjectFile *Obj, ScopedPrinter &Writer)
       : ObjDumper(Writer), Obj(Obj), Writer(Writer), Types(100) {}
 
   void printFileHeaders() override;
   void printSections() override;
   void printRelocations() override;
   void printSymbols() override;
   void printDynamicSymbols() override;
   void printUnwindInfo() override;
+
+  void printNeededLibraries() override;
+
   void printCOFFImports() override;
   void printCOFFExports() override;
   void printCOFFDirectives() override;
   void printCOFFBaseReloc() override;
   void printCOFFDebugDirectory() override;
   void printCOFFResources() override;
   void printCOFFLoadConfig() override;
   void printCodeViewDebugInfo() override;
void COFFDumper::printUnwindInfo() {
   }
   default:
     W.printEnum("unsupported Image Machine", Obj->getMachine(),
                 makeArrayRef(ImageFileMachineType));
     break;
   }
 }
 
+void COFFDumper::printNeededLibraries() {
+  ListScope D(W, "NeededLibraries");
+
+  using LibsTy = std::vector<StringRef>;
+  LibsTy Libs;
+
+  for (const ImportDirectoryEntryRef &DirRef : Obj->import_directories()) {
+    StringRef Name;
+    if (!DirRef.getName(Name))
+      Libs.push_back(Name);
+  }
+
+  std::stable_sort(Libs.begin(), Libs.end());
+
+  for (const auto &L : Libs) {
+    outs() << "  " << L << "\n";
+  }
+}
+
 void COFFDumper::printImportedSymbols(
     iterator_range<imported_symbol_iterator> Range) {
   for (const ImportedSymbolRef &I : Range) {
     StringRef Sym;
     error(I.getSymbolName(Sym));
     uint16_t Ordinal;
     error(I.getOrdinal(Ordinal));
     W.printNumber("Symbol", Sym, Ordinal);