From issue #7400 and:
https://bitbucket.org/wlav/cppyy-backend/commits/4a2d9dfa1a6f8b7cf8e8033eadfffdd0dc9f79a5
https://bitbucket.org/wlav/cpycppyy/commits/8a2af080d20c093cbe21128f13c3ad72ea5f9599

Fix #7890.

Co-authored-by: Axel Naumann <Axel.Naumann@cern.ch>

In CMake, variables like CMAKE_CXX_FLAGS_RELEASE etc should be cache
variables, so users can set them from outside. ROOT, however, FORCE
overwrote them, so users cannot change anything.
Now, the variables are not set by ROOT at all, we use the CMake
defaults.
It is fine to append or replace substrings, but the variables should NOT
be overwritten to give users some options.

In case ROOT wants to move away from CMake defaults, it can be done like
this:
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e40b84a920..ab41612006 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -29,6 +29,11 @@ endforeach()

 include(cmake/modules/CaptureCommandLine.cmake)

+set(CMAKE_CXX_FLAGS_DEBUG_INIT "-O1 -g")
+set(CMAKE_CXX_FLAGS_ASSERT_INIT "-O2 -g")
+
 project(ROOT)

- Replace `long` types by `Longptr_t`
- Fix pointer formatting (use `%zx` and `size_t` for architecture dependent format)

Fixes #7829 finally

Fixes #7829 partially, missing integration into Describe

This fixes issue-7081, as now, with the correct spelling
of the env var, the build-ROOTSYS is picked up by
roottest.

Reactivate the doxygen TOC for \page

Co-authored-by: Philippe Canal <pcanal@fnal.gov>

Std library types are picked up by rootcling as TClasses. If there is no
RField specialization for them, they are passed to the RClassField
constructor. This led to accidental support of those std types by
RNTuple. For some types, this appeared to be benign (e.g. std::pair) but
for others there were errors (e.g. std::optional).

Change the RClassField constructor to throw an exception if any std type
is passed in.

If such mode configured, catch thread id for ProcessEvents
and use that id to process RWebWindow callbacks. Mainly dedicated
for the python, but also can be used in other apps

Indicates that python runs special thread where ProcessEvents called
WebGui has to these ProcessEvents for such calls

Using WebGui.ExternalProcessEvents: yes in rootrc.
In such mode RWebWindow ignores assigned thread id and just executes
functionality in calling thread (which is dangerous)

In this time server will not react on any other user actions,
therefore just block UI with modal message

Means when top folder is shown, one always sees list of files displayed
Therefore when any ROOT file is opened, RBrowser just changes to
its top folder

Provide button to toggle between current directory and list of opened
files

Indicies used for handling many elements with same name in browser,
but do not (yet) supported when configuring working path

ROOT will try to find external version first and
only if fail fallback to builtin variant.

For `std::string`, we have both a TClass and a TDataType (as it is a typedef).
We should prefer the TClass (which fixes issue #7169), but not at the cost
of calling `TClass::GetClass()` first: that is just too slow. So instead,
check for "is it a datatype, not numeric, do we have a TClass?" which will
still prefer the TClass even if *also* a TDataType exists.

Provide documentation!

..rather than building the leaf name "by hand".