Copy from 5.34 patches optimisation in HistFactory (FlexibleInt. and PicewiseInt.)
Apply a patch from Bertrand to fix warning C4436 from VS
(dynamic_cast from virtual base 'class1' to 'class2' in constructor or destructor )
Syncronize with our clang repo: minimize diffs.
Revert "Fix typo a la llvm coding convention."

This reverts commit ce6de2269830de3e0eb72dcade4826cb5f3538ab.
Revert "Fix fatal typo"

This reverts commit 84cb95c01813a49ce278614b7180de005665041d.
Revert "Search the symbol in all available dylibs (ROOT-6015)."

This reverts commit 706b8a1c17c780fb5d28ad2586a8842e45b7f051.
DLRT_DEFAULT is alreday searched; it is one of the OpenedHandles.
fix typos.
Use LC_ALL to unfrenchify (ROOT-6017).