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.cxx

@@ -0,0 +1,27 @@
+/* Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+   file Copyright.txt or https://cmake.org/licensing for details.  */
+
+#include "cmLinkLineComputer.h"
+#include "cmOutputConverter.h"
+
+cmLinkLineComputer::cmLinkLineComputer(cmState::Directory stateDir)
+  : StateDir(stateDir)
+{
+}
+
+cmLinkLineComputer::~cmLinkLineComputer()
+{
+}
+
+std::string cmLinkLineComputer::ConvertToLinkReference(
+  std::string const& lib) const
+{
+  std::string relLib = lib;
+
+  if (cmOutputConverter::ContainedInDirectory(
+        this->StateDir.GetCurrentBinary(), lib, this->StateDir)) {
+    relLib = cmOutputConverter::ForceToRelativePath(
+      this->StateDir.GetCurrentBinary(), lib);
+  }
+  return relLib;
+}