Fix warnings
ReadStream, 'non-strict' mode for TNtuple/TNtupleD.
Fix a comment.
Improve an error message and comments.
ROOT-6026: handle Doxygen I/O comments correctly
New example
Add exception handling compiler flag on Windows
Comment.
Merge branch 'master' of https://root.cern.ch/git/root
Correct misleading name of error emitter in error message
Must emit static variables from template instantiations (ROOT-6015).

This correpsonds to the call to CodeGen::HandleCXXStaticMemberVarInstantiation().
Failure in template instantiation is a lookup failure (ROOT-6070).

(cherry picked from commit 4c32242c51a35c6e2f616457083927a68822a699)
(cherry picked from commit a0222efc70bd60a8c3bceb5e357630c81f5df3c8)
Inform TClass about class definitions of fwd decls (ROOT-6012).
Prevent div by zero in TFile::CpProgress
New example
Use SSE also for 32bit.

Without, 387's "extended precision" kicks in unpredictably, possibly changing the results of fp ops.
As GCC says: "The resulting code should be considerably faster in the majority of cases and avoid the numerical instability problems of 387 code, but may break some existing code that expects temporaries to be 80 bits."

(cherry picked from commit 686f22cbf75a3119df86f8ff2d01701b65ba707f)
New example
Delay eval of CLINGCXXFLAGS: llvm-config is not yet built.
::Form -> TString::Form(at)

(cherry picked from commit 97cd75e145d8e9d934d2493acb42b585ca554cb9)

Conflicts:
	core/winnt/src/TWinNTSystem.cxx
	io/io/src/TDirectoryFile.cxx
Remove help for builtin-llvm: it is meaningless for non-devs.