This is a follow up of f5249760 and a fix for ROOT-10632

Fix discrepancy with find_package_handle_standard_args and  name of the calling package (CMake 3.17)

While gtk sources are in ROOT source directory, one needs
to specify includes from ${CMAKE_SOURCE_DIR}.
This is not good, while dictionaty intend to be build only from
${CMAKE_BUILD_DIR}/include.

Was required in previous usage, now they are fully internal

One need virtual method in TVirtualIndex to verify if it can be
applied to TTree. Otherwise one has to link Tree lib again TreePlayer and
Hist to access TTreeFormula methods, making circular dependency

[ROOT-10647] The "section" argument of the function was ignored.

This patch also instruct the build system to not copy {libc,std}.modulemap in
OSX because the standard libraries are already modularized.

Fixes a regression introduced by root-project/root@603a1c3e96

On linux, the compiler flags are cache variables, i.e. they can be
overridden by the user. On Mac, that wasn't the case.

rootcling writes dependency information which is never read/used when
loading the rdict file.

Otherwise one has to set dependency from ProofPlayer lib

Let use this enum in win32gdk to avoid direct dependency from
Gui library there

It is a proper place for virtual class

Includes are from libs, which are not in Hist library dependency list

They were not really used, but were introducing wrong dependency

This makes possible to use them via TVirtualTreePlayer and
one do not explicitly depend in TreePlayer library when building gui classes

- captureStdErr cannot be called without a corresponding GetCapturedStdErr.
  avoid useless capturedStdErr call
- avoid producing a TTree with the kEntriesShuffled bit set in friend test

...and add a test. This fixes ROOT-9556.

The TTree::kEntriesReshuffled bit signals that a TTree is the output
of the processing of another TTree, and its entries are reshuffled
w.r.t. to the original TTree. A TTree with this bit set should not
add friends nor should be added as a friend, because it is very likely
that the original event-by-event correspondence has been broken.

Users can manually unset the bit to force the original behavior.

Previously, desping a warning message stating that the TFriendElement
"could not be added", TTree was adding the friend anyway, even if the
actual friend TTree object was not found in the file. This could lead
to missing data or stale data being read.