This lead to corrupted cluster range tables (and thus failure in dataframe_snapshot)
when importing the cluster table into a TTree that was just read from file and
has a cluster table.

This reverts commit 2b3e3b5d2b90807c167b19b22f3624290c345ee7.

root_multicore_threadExecutor is failing/timeout sometimes.

This reverts commit 91e15d338113272919cc055b29e75f708eab2df6.

  There are some codes compiled at the start up time. For example,
    - #include \"cling/Interpreter/RuntimeUniverse.h\"
    - #include \"cling/Interpreter/DynamicLookupRuntimeUniverse.h\"
    - namespace cling { class Interpreter; namespace runtime { Interpreter* gCling }}}
    - PrintValue
  These are passed to Cling as string and initialized at the start up time.  So I think it makes sense to reduce top-level global variables, #includes and virtual functions.

  1. Global variables
    If we break at emitModule, we can get a list of global variables and functions which are actually deserialized. These include functions, variables, STL classes and all the functions derives from them.
 I tried to change them to for example constexpr, so that it's processed at compile time.
  2. Eagerly Deserialized decls
    Thanks to @Axel 's hint and tip, we could minimize eagerly deserialized decls deserialized in ASTReader::PassInterestingDeclsToConsumer. We already removed most of eagerly deserialized decls (Some are remaining to be removed, some are hard to remove and some don't cost a lot).

  So far, we got 9.2% of cpu time improvement and 8.8% of memory improvement at start up time in release build.

  - root.exe -q -l
    - master
      cpu time = 0.09186914285714286 sec (average of 7 times)
      res  memory = 142.008 Mbytes

    - HEAD
      cpu time = 0.08337842857142856 sec
      res  memory = 129.508 Mbytes

  - hsimple.C
  Improved by 13% of cpu time and 8.5% of memory
    - master
      cpu time = 0.0954708 sec (average)
      res  memory = 142.891 Mbytes

    - HEAD
      cpu time = 0.0833258 sec
      res  memory = 130.73 Mbytes

  With modules
    - Improvement by 17.7% in cputime and 2% in memory on root.exe -q -l
    (For memory, small improvement is because most of the memory is taken by LoadModules)
    - With this patch, modules is 11.2% slower in cpu time and 6% better in residential memory.

Substitution of '.' with '_' should only happen when the dot is
in the middle of the name.

This warning was first seen in rootbench:
root-benchmark/BUILDTYPE/Release/COMPILER/gcc62/LABEL/performance-cc7/build/include/ROOT/TDFActionHelpers.hxx:745:34:
warning: parameter ‘slot’ set but not used [-Wunused-but-set-parameter]
    void SetBranches(unsigned int slot, BranchTypes&... values, StaticSeq<S...> /*dummy*/)
                                  ^~~~

For in-tree builds we need Options.inc to be tablegen-ed before
building clingInterpreter library.

This reverts commit e1ad7892 since
there are still conflicts with the name arrow in the tutorials.

For example std::vector::at

this is done temporarily to test the new code and avoid to touch the
infrastructure.

as this latter feature is now useless.

and avoid to include Arrow headers within the TArrowDS header, therewith
in the PCH.