[lld-link] Change config and driver to unique_ptr

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

Reviewed By: mstorsjo

Differential Revision: https://reviews.llvm.org/D116996

lld/COFF/Config.h

@@ -282,7 +282,7 @@ struct Configuration {
   bool stdcallFixup = false;
 };
 
-extern Configuration *config;
+extern std::unique_ptr<Configuration> config;
 
 } // namespace coff
 } // namespace lld

lld/COFF/Driver.cpp

@@ -60,8 +60,8 @@ 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) {
@@ -80,8 +80,8 @@ bool link(ArrayRef<const char *> args, bool canExitEarly, raw_ostream &stdoutOS,
   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);
 

lld/COFF/Driver.h

@@ -30,8 +30,7 @@
 namespace lld {
 namespace coff {
 
-class LinkerDriver;
-extern LinkerDriver *driver;
+extern std::unique_ptr<class LinkerDriver> driver;
 
 using llvm::COFF::MachineTypes;
 using llvm::COFF::WindowsSubsystem;