Re-ordered some statements in the main CMakeLists.txt file. The main purpose here was to move the

inclusion of cmake/externals.cmake after the ATLAS externals project was found, when building
Gaudi in the ATLAS software stack. This allows the ATLAS externals project to direct the Gaudi
code towards the ranges_v3 headers that it should be picking up.

CMakeLists.txt

 CMAKE_MINIMUM_REQUIRED(VERSION 2.8.5)
 
+# Configurable options for building Gaudi in the ATLAS software stack:
+option( GAUDI_ATLAS "Enable ATLAS-specific settings" OFF )
+set( GAUDI_ATLAS_BASE_PROJECT "AtlasExternals" CACHE STRING
+   "Name of the ATLAS base project to build Gaudi against" )
+
 # Ensure that we can find GaudiProjectConfig.cmake
 # (this works only for projects embedding GaudiProjectConfig.cmake)
 if(NOT GaudiProject_DIR AND ("$ENV{GaudiProject_DIR}" STREQUAL ""))
   set(GaudiProject_DIR ${CMAKE_SOURCE_DIR}/cmake)
 endif()
 
-include(${CMAKE_SOURCE_DIR}/cmake/externals.cmake)
-
 #---------------------------------------------------------------
 # Load macros and functions for Gaudi-based projects
 find_package(GaudiProject)
 #---------------------------------------------------------------
 
-option( GAUDI_ATLAS "Enable ATLAS-specific settings" OFF )
-set( GAUDI_ATLAS_BASE_PROJECT "AtlasExternals" CACHE STRING
-   "Name of the ATLAS base project to build Gaudi against" )
-
 # Base Gaudi on "the ATLAS base project" (AtlasExternals by default) when
 # building for ATLAS:
 if( GAUDI_ATLAS )
@@ -24,6 +23,9 @@ if( GAUDI_ATLAS )
    gaudi_ctest_setup() # Needed for correct CTest usage in this setup
 endif()
 
+# Find/set up some needed externals:
+include(${CMAKE_SOURCE_DIR}/cmake/externals.cmake)
+
 # Declare project name and version
 gaudi_project(Gaudi v28r1)