ROOT_GENERATE_DICTIONARY allows to specify dependencies, but we currently
don't actually specify those. As we need this for getting the module
dependencies right (as we can't build missing modules on demand), we should
add those dependencies here. Then those dependencies propagate to the
rootcling invocation which will in the future also generate the C++ module
for the selected dictionary.

This is already the case in CMake builds, adding it to make
behavior between build types more uniform. The option is not
added for ICC since it does not have such option and will
generate warnings about ignored flags. Also remove some old
unused options.

This is already the case in the CMake build, enabling the same on
classic makes the behavior more uniform across build types.

This option is already set to OFF in interpreter/llvm/CMakeLists.txt.

The options are obsolete since the last LLVM upgrade.

Adding these unused options generates warnings in the classic build:
http://cdash.cern.ch/viewBuildError.php?type=1&buildid=372656

Also remove add_definitions(-pthread) from CMakeLists.txt.
This is not the right function to use to add the flag, and
it is already taken care of by cmake/modules/CheckCompiler.cmake
in any case.

Warning:
root/core/rootcling_stage1/src/rootcling_stage1.cxx(38):
	warning #69: integer conversion resulted in truncation

   auto dummyVal = (int)(long)&usedToIdentifyRootClingByDlSym;
                    ^^^

The method above uses a cast to long, followed by a cast to int,
which results in a truncation. That is harmless, since the value
is never used, but generates a compiler warning with ICC 17. This
commit avoids the warning by storing the address of the same symbol
in a static variable instead.

Reference:
http://cdash.cern.ch/viewBuildError.php?type=1&buildid=372731

and don't create fake directories to store histograms.

This reverts commit c4978f1b.

The reason to revert is that this breaks offline builds of ROOT,
since no check for an active internet connection is performed in
in the build system.

There is no equivalent 'gsl' option, so since mathcore is the main
consumer of GSL, it makes sense to enable the builtin version when
the user requests to build mathmore rather than disabling mathmore.

There is no support for thread_local on macOS, so variables with
thread local storage must use the ROOT macros for this purpose.

Found by coverity.

* Extended DNN implementation to support weighting of training samples and implemented the weighting functionality in the CPU backend.

* Extended DNN tests to cover sample weighting functionality.

* Added event weight handling to CUDA backend.

* Added event weight handling to reference backend.

* Removed unused file DataLoader.cxx

* clang-format

This was not really rehired anyway .