Wrap build of DDG4 in a valid runtime environment
In some cases ROOT requires a valid runtime environment to be able to load libCore.so
.
Similar to what happened in Gaudi (see gaudi/Gaudi!1419 (merged)), DD4hep invocation of listcomponents
needs more than just LD_LIBRARY_PATH
if the plugin library requires the initialization of the ROOT interpreter.
This MR wraps the invocation of cmake --build
performed by ExternalProject_Add
in an environment that is good enough for libCore.so
to initialize without problems.