ENH: On VMS use _dir and _tmp, not .dir and .tmp

The VMS posix path emulation does not handle multiple '.' characters in
file names in all cases.  This avoids adding extra '.'s to file and
directory names for target directories and generated files.

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -2158,7 +2158,11 @@ cmLocalUnixMakefileGenerator3
 {
   std::string dir = cmake::GetCMakeFilesDirectoryPostSlash();
   dir += target.GetName();
+#if defined(__VMS)
+  dir += "_dir";
+#else
   dir += ".dir";
+#endif
   return dir;
 }