Cherry-pick "Merge branch 'ROOTBuildFixes-1.0-20190124' into '1.0'" into master

ROOT Build Fixes, 1.0 branch (2019.01.24.)

See merge request !429 (merged)

(cherry picked from commit 5d0b08a2)

• e6fb1370 Made it possible to use generator expressions on configure.sh.
• 8a58eac4 Updated the build of Davix and ROOT so that ROOT would find Davix.