Made it possible to use SITEROOT != "/afs/cern.ch" during the build.

The CMake code was unfortunately not acknowledging the setting of that
variable in the build environment before now.

Database/ConnectionManagement/AtlasAuthentication/CMakeLists.txt

-# $Id: CMakeLists.txt 720646 2016-01-29 14:01:10Z krasznaa $
+# Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 #
 # Build configuration for package AtlasAuthentication.
 #
@@ -6,11 +6,6 @@
 # Declare the package's name:
 atlas_subdir( AtlasAuthentication )
 
-# If we are in release rebuilding mode, stop here:
-if( ATLAS_RELEASE_MODE )
-   return()
-endif()
-
 # Install the local file(s) of the package:
 atlas_install_xmls( data/*.xml )
 atlas_install_runtime( data/dbreplica.config )
@@ -18,15 +13,15 @@ atlas_install_scripts( share/setupLocalDBReplica_CERN.sh )
 
 # Find the ATLAS externals area:
 if( NOT SITEROOT )
-   if( ENV{SITEROOT} )
-      set( SITEROOT $ENV{SITEROOT} )
+   if( NOT "$ENV{SITEROOT}" STREQUAL "" )
+      set( SITEROOT "$ENV{SITEROOT}" )
    else()
       set( SITEROOT "/afs/cern.ch" )
    endif()
 endif()
 if( NOT ATLAS_EXTERNAL )
-   if( ENV{ATLAS_EXTERNAL} )
-      set( ATLAS_EXTERNAL $ENV{ATLAS_EXTERNAL} )
+   if( NOT "$ENV{ATLAS_EXTERNAL}" STREQUAL "" )
+      set( ATLAS_EXTERNAL "$ENV{ATLAS_EXTERNAL}" )
    else()
       set( ATLAS_EXTERNAL "${SITEROOT}/atlas/offline/external" )
    endif()

External/AtlasDataArea/CMakeLists.txt

-# $Id: CMakeLists.txt 768579 2016-08-18 09:20:20Z alibrari $
+# Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
 
 # Declare the name of the package:
 atlas_subdir( AtlasDataArea )
 
-# If we are in release rebuilding mode, stop here:
-if( ATLAS_RELEASE_MODE )
-   return()
-endif()
-
 # Find the ATLAS ReleaseData area:
 if( NOT SITEROOT )
-   if( ENV{SITEROOT} )
-      set( SITEROOT $ENV{SITEROOT} )
+   if( NOT "$ENV{SITEROOT}" STREQUAL "" )
+      set( SITEROOT "$ENV{SITEROOT}" )
    else()
       set( SITEROOT "/afs/cern.ch" )
    endif()
 endif()
 if( NOT ATLAS_RELEASEDATA )
-   if( ENV{ATLAS_RELEASEDATA} )
-      set( ATLAS_RELEASEDATA $ENV{ATLAS_RELEASEDATA} )
+   if( NOT "$ENV{ATLAS_RELEASEDATA}" STREQUAL "" )
+      set( ATLAS_RELEASEDATA "$ENV{ATLAS_RELEASEDATA}" )
    else()
       set( ATLAS_RELEASEDATA "${SITEROOT}/atlas/offline/ReleaseData" )
    endif()

External/FWDet/TwissFiles/CMakeLists.txt

+# Copyright (C) 2002-2021 CERN for the benefit of the ATLAS collaboration
+
 # Declare the name of the package:
 atlas_subdir( TwissFiles )
 
-# If we are in release rebuilding mode, stop here:
-if( ATLAS_RELEASE_MODE )
-   return()
-endif()
-
 # Find the ATLAS TwissFiles area:
 if( NOT SITEROOT )
-   if( ENV{SITEROOT} )
-      set( SITEROOT $ENV{SITEROOT} )
+   if( NOT "$ENV{SITEROOT}" STREQUAL "" )
+      set( SITEROOT "$ENV{SITEROOT}" )
    else()
       set( SITEROOT "/afs/cern.ch" )
    endif()
 endif()
 if( NOT ATLAS_TWISSFILES )
-   if( ENV{ATLAS_TWISSFILES} )
-      set( ATLAS_TWISSFILES $ENV{ATLAS_TWISSFILES} )
+   if( NOT "$ENV{ATLAS_TWISSFILES}" STREQUAL "" )
+      set( ATLAS_TWISSFILES "$ENV{ATLAS_TWISSFILES}" )
    else()
       set( ATLAS_TWISSFILES "${SITEROOT}/atlas/offline/external/TwissFiles" )
    endif()