support for sanitizer libraries was dropped with !986

While the compiler options for using sanitizers can be set from outside (e.g. via special build types as in lhcb-core/lcg-toolchains!30 (merged)) we also have to be able to keep suppression files in the project repository an may be install them to make them available downstream.

For the record, I managed to fix (at least part of) the build of Gaudi with lhcb/Gaudi@f37b5c88, but that's not enough for downstream projects as those variables are not propagated to downstream projects.