The INCLUDE_DIRECTORIES property only became available in
CMake 3.11, so we have to use COMPILE_FLAGS instead, which
is already available in our required version (CMake 3.4.3).

Note: The ROOT_ARCHITECTURE value of win32old is not found anywhere
else in the code, and the files referred to don't exist anymore, so
the obsolete linkdef file has been removed too.

It is fixing:
..root/tree/dataframe/src/RDataFrame.cxx:789:6: error: reference to 'RDF' is ambiguous
   : RDF::RInterface<RDFDetail::RLoopManager>(
     ^
In module 'ROOTDataFrame' imported ..root/tree/dataframe/src/RDataFrame.cxx:14:
..include/ROOT/RCutFlowReport.hxx:29:11: note: candidate found by name lookup is 'ROOT::RDF'
namespace RDF {
          ^
..root/tree/dataframe/src/RDataFrame.cxx:721:11: note: candidate found by name lookup is 'ROOT::Detail::RDF'
namespace RDF {
          ^
..tree/dataframe/src/RDataFrame.cxx:789:11: error: member initializer (null) does not name a non-static data member or base class
   : RDF::RInterface<RDFDetail::RLoopManager>(
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This reverts commit 80b1a73b.

The patch triggers a pre-existing bug on fedora28 and gcc8.1

This is a better implementation over doing #ifdef R__USE__CXXMODULES
everywhere.

Such pictures can (now) be displayed with `\macro_image (picture_name.png[.pdf])`

where possible without too many hacks.

reorder images and code, add output, make sure canvases can be
properly saved. Also trim out useless code to minimise the examples.

if the size is bigger than the default value. Document better the behaviour, too.

This error: http://cdash.cern.ch/viewBuildError.php?buildid=567476
was caused because modules couldn't merge definition of struct __pthread_internal_list

This is to enable the supression of file modification error and module
relocation error provided by Clang. File modification error is emitted
when source file is changed after implicit pcm was generated, but what
we want for Clang is to just re-generate new pcm and replace it, rather than
emitting errors.

but rather for the missing dictionary of T given the way in which we
treat unique_ptrs.

Fixes builds with command line tools and macos 10.14.

Previously, [system] was used to mark modules which were supporsed be
implicitly built by rootcling for runtime modules. This was a workaround, and it was causing
SourceLocation error in cxxmodules as it is also using the same
modulemap.

To remove the workaround, we are introducing a new convention that modules
start with ROOT_ is treated as "ROOT system modules", which can be build
implicitly.