cmLinkLineComputer: Extract from cmLocalGenerator

CMake has several classes which have too many responsibilities.
cmLocalGenerator is one of them.  Start to extract the link line
computation.  Create generator-specific implementations of the interface
to account for generator-specific behavior.

Unfortunately MSVC60 has different behavior to everything else and CMake
still generates makefiles for it.  Isolate it with MSVC60-specific
names.

Source/cmLinkLineComputer.h

@@ -0,0 +1,21 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#ifndef cmLinkLineComputer_h
+#define cmLinkLineComputer_h
+
+#include "cmState.h"
+
+class cmLinkLineComputer
+{
+public:
+  cmLinkLineComputer(cmState::Directory stateDir);
+  virtual ~cmLinkLineComputer();
+
+  virtual std::string ConvertToLinkReference(std::string const& input) const;
+
+private:
+  cmState::Directory StateDir;
+};
+
+#endif