[lld-link] Change config and driver to unique_ptr

[MaskRay]

Summary

Similar to D116143. My x86-64 lld is ~5KiB smaller.

[mstorsjo]

Looks sensible to me based on the referenced patch.

lld/COFF/Config.h

struct Configuration {
   bool swaprunNet = false;
   bool thinLTOEmitImportsFiles;
   bool thinLTOIndexOnly;
   bool autoImport = false;
   bool pseudoRelocs = false;
   bool stdcallFixup = false;
 };
 
-extern Configuration *config;
+extern std::unique_ptr<Configuration> config;
 
 } // namespace coff
 } // namespace lld
 
 #endif

lld/COFF/Driver.h

 #include "llvm/Support/TarWriter.h"
 #include <memory>
 #include <set>
 #include <vector>
 
 namespace lld {
 namespace coff {
 
-class LinkerDriver;
-extern LinkerDriver *driver;
+extern std::unique_ptr<class LinkerDriver> driver;
 
 using llvm::COFF::MachineTypes;
 using llvm::COFF::WindowsSubsystem;
 using llvm::Optional;
 
 class COFFOptTable : public llvm::opt::OptTable {
 public:
   COFFOptTable();

lld/COFF/Driver.cpp

 using namespace llvm;
 using namespace llvm::object;
 using namespace llvm::COFF;
 using namespace llvm::sys;
 
 namespace lld {
 namespace coff {
 
-Configuration *config;
-LinkerDriver *driver;
+std::unique_ptr<Configuration> config;
+std::unique_ptr<LinkerDriver> driver;
 
 bool link(ArrayRef<const char *> args, bool canExitEarly, raw_ostream &stdoutOS,
           raw_ostream &stderrOS) {
   lld::stdoutOS = &stdoutOS;
   lld::stderrOS = &stderrOS;
 
   errorHandler().cleanupCallback = []() {
     freeArena();
   };
 
   errorHandler().logName = args::getFilenameWithoutExe(args[0]);
   errorHandler().errorLimitExceededMsg =
       "too many errors emitted, stopping now"
       " (use /errorlimit:0 to see all errors)";
   errorHandler().exitEarly = canExitEarly;
   stderrOS.enable_colors(stderrOS.has_colors());
 
   COFFLinkerContext ctx;
-  config = make<Configuration>();
-  driver = make<LinkerDriver>(ctx);
+  config = std::make_unique<Configuration>();
+  driver = std::make_unique<LinkerDriver>(ctx);
 
   driver->linkerMain(args);
 
   // Call exit() if we can to avoid calling destructors.
   if (canExitEarly)
     exitLld(errorCount() ? 1 : 0);
 
   bool ret = errorCount() == 0;