Allow include of G4 headers with or without 'Geant4/' prefix

CMakeLists.txt

@@ -7,6 +7,11 @@ find_package(GaudiProject)
 gaudi_project(Geant4 v106r2p4
               DATA Geant4Files VERSION ${GEANT4FILES_VERSION})
 
+# Compatibility with standard Geant4 installation
+file(APPEND "${CMAKE_CONFIG_OUTPUT_DIRECTORY}/${CMAKE_PROJECT_NAME}PlatformConfig.cmake"
+  "\nset(${CMAKE_PROJECT_NAME}_INCLUDE_DIRS \${_dir}/include/Geant4 \${${CMAKE_PROJECT_NAME}_INCLUDE_DIRS})\n"
+)
+
 # FIXME: hack for compatibility with CMT build
 file(WRITE ${CMAKE_BINARY_DIR}/dummy.cpp "")
 link_directories(${CMAKE_INSTALL_PREFIX}/lib)