CI Add Doxygen as dependency

.gitlab-ci.d/init_x86_64.sh

@@ -88,6 +88,13 @@ export CMAKE_PREFIX_PATH="$ROOTSYS:$CMAKE_PREFIX_PATH"
 export Ninja_HOME=${CLICREPO}/software/Ninja/1.7.2/${BUILD_FLAVOUR}
 export PATH="$Ninja_HOME:$PATH"
 
+#--------------------------------------------------------------------------------
+#     Doxygen
+#--------------------------------------------------------------------------------
+
+export Doxygen_HOME=${SFTREPO}/lcg/releases/doxygen/1.8.11-ae1d3/${BUILD_FLAVOUR}/bin/
+export PATH="$Doxygen_HOME:$PATH"
+
 #--------------------------------------------------------------------------------
 #     Git
 #--------------------------------------------------------------------------------