Driver: support -fuse-ld= on cross windows

Update the linker selection to support the `-fuse-ld=` option for selecting a
linker.

llvm-svn: 251493
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 44609aa..1c6f86f 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -9750,8 +9750,7 @@
     }
   }
 
-  const std::string Linker = TC.GetProgramPath("ld");
-  Exec = Args.MakeArgString(Linker);
+  Exec = Args.MakeArgString(TC.GetLinkerPath());
 
   C.addCommand(llvm::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs));
 }