Cppyy supports C++11.

Revert PR3075: it causes
CMakeFiles/ROOTDataFrame.dir/src/RSqliteDS.cxx.o: In function `(anonymous namespace)::VfsRdOnlyRead(sqlite3_file*, void*, int, long long)':
RSqliteDS.cxx:(.text+0x237): undefined reference to `Davix::DavPosix::pread(Davix_fd*, void*, unsigned long, long, Davix::DavixError**)'

and many more.

This reverts commit 84108b50.

This reverts commit d6e02859.

This reverts commit f9201586.

It breaks the build, as doc generation for these tools imports PyROOT before it has been built.

When Davix is builtin, libdavix is static and the symbols get copied
both into RDAVIX and ROOTDataFrame, and clash at runtime because there
are multiple copies of the same symbols. To resolve this problem, we
link ROOTDataFrame to RDAVIX only, but for that we have to propagate the
include directory by using PUBLIC linking explicitly. Also, since the
header for SQLite is not needed during dictionary generation, we can
remove it from the DICTIONARY_OPTIONS of ROOTDataFrame as well.

Fixes: ROOT-9845

This reverts commit 7a3ab578,
as it fails on Mac OS with either duplicate or missing symbols.
Related issue: https://github.com/xrootd/xrootd/issues/760.

TTreeProcessorMT does not guarantee that TTreeReader::GetCurrentEntry
returns the global entry number of the underlying dataset.
RDF, however, needs a unique entry identifier to use for Filter/Define
cache invalidation, so for MT runs we now use an atomic counter.

As a consequence, in MT runs `rdfentry_` is now an arbitrary integer
with no connection to the underlying ROOT dataset.

This reverts commit 10025483.

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The dnn_cuda library is only an intermediate library that is not
meant to be installed with ROOT, so it needs to be static since
TMVA needs to export its dependencies and if this library is shared
the dependency won't be there after a `make install'. Therefore the
error in CMake:

CMake Error: install(EXPORT "ROOTExports" ...) includes target "TMVA"
which requires target "dnn_cuda" that is not in the export set.