Pre-compute object file names before Makefile generation

Add a virtual cmGlobalGenerator::ComputeTargetObjects method invoked
during cmGeneratorTarget construction.  Implement it in the Makefile
generator to pre-compute all object file names for each target.  Use
the results during generation instead of re-computing it later.

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -2008,45 +2008,6 @@ void cmLocalUnixMakefileGenerator3
     }
 }
 
-//----------------------------------------------------------------------------
-std::string
-cmLocalUnixMakefileGenerator3
-::GetObjectFileName(cmTarget& target,
-                    const cmSourceFile& source,
-                    std::string* nameWithoutTargetDir,
-                    bool* hasSourceExtension)
-{
-  // Make sure we never hit this old case.
-  if(source.GetProperty("MACOSX_PACKAGE_LOCATION"))
-    {
-    std::string msg = "MACOSX_PACKAGE_LOCATION set on source file: ";
-    msg += source.GetFullPath();
-    this->GetMakefile()->IssueMessage(cmake::INTERNAL_ERROR,
-                                      msg.c_str());
-    }
-
-  // Start with the target directory.
-  std::string obj = this->GetTargetDirectory(target);
-  obj += "/";
-
-  // Get the object file name without the target directory.
-  std::string dir_max;
-  dir_max += this->Makefile->GetCurrentOutputDirectory();
-  dir_max += "/";
-  dir_max += obj;
-  std::string objectName =
-    this->GetObjectFileNameWithoutTarget(source, dir_max,
-                                         hasSourceExtension);
-  if(nameWithoutTargetDir)
-    {
-    *nameWithoutTargetDir = objectName;
-    }
-
-  // Append the object name to the target directory.
-  obj += objectName;
-  return obj;
-}
-
 //----------------------------------------------------------------------------
 void cmLocalUnixMakefileGenerator3::WriteDisclaimer(std::ostream& os)
 {