`TDirectory::mkdir` returns a `nullptr` in case the directory already
exists. This can happen in case the destination ROOT file already
exists.

* do not explicitly specify details:: when it is not needed
* change a 'zip::const_range' into a 'zip::range' as the content
  is already const (and this avoids an internal compiler error
  downstream)
* define two macros to factor out the pragmas needed to exclude
  a false positive clang diagnostic, and update the existing
  exclusion to use these.
  Note that current clang trunk is fixed, see https://bugs.llvm.org/show_bug.cgi?id=42104,
  so starting with clang 9, the diagnostic should no longer
  have the false positive.

Gitlab CI authored Aug 17, 2019 and Christopher Rob Jones committed Aug 17, 2019

patch generated by https://gitlab.cern.ch/jonrob/Gaudi/-/jobs/5192816

In case no new file name was set, e.g. by not calling `io_update_all`,
do not try to open a file with an empty file name. This is a common
use-case in case the mother process is continuing to use its initial set
of ROOT files.

* fixes a (correct!) gcc9 warning about deprecated implicit assignment
  operator -- in general, either both copy constructor and assignment
  should be defined, or neither

- improvements to build options for LCG96
- bug fixes for a few sanitizer found issues
- preliminary clang support for sanitizers

Closes #56

that interface does not exist in recent versions of LHCb

see gaudi/Gaudi#75

Closes #83

The change was introduced with !904

Closes #70

Closes #75 and #87

Closes #88

Closes #86