Add missing licence header.

Modules/GenerateExportHeader.cmake

@@ -98,6 +98,20 @@
 #
 # This will cause the export macros to expand to nothing when building the static library.
 
+
+#=============================================================================
+# Copyright 2011 Stephen Kelly <[email protected]>
+#
+# Distributed under the OSI-approved BSD License (the "License");
+# see accompanying file Copyright.txt for details.
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+# (To distribute this file outside of CMake, substitute the full
+#  License text for the above reference.)
+
 include(CMakeParseArguments)
 include(CheckCXXCompilerFlag)