If at least C++14 is available, including "RMakeUnique.hxx" is equivalent
to "memory".

thanks to Enrico for providing most of the text.

This reverts part of commit 5059f594.

this is a hook the TDF "data processing framework" triggers.

this may be useful to allow users to perform operations when
work stealing happens in order to restore the state the "stolen" work item
found before starting.

this is the method which is called first by the TDF and it makes sense
to make room for the cursor at this point.

it's a very clear and general concept which applies perfectly in the
context of the TDataSource. Thanks to J. Blomer for mentioning it
in the first place!

then the one that was used to build cling and finally the one
in the absolute path (e.g. usr/bin/g++)

XCode 9 introduces in C++11 mode an std::string_view (in experiemental) and the new std::string constructor
with an std::string_view argument.  This means that it would require the explicit conversion from
TString to std::string to remove ambiguity.  However it seems to not honor this explicit conversion.
Until we figure out whether this is a deficiency or a feature, work-around it by using TString::Data

Previously the modules were only a environment variable, so we never
had any CMake code that added the correct dependencies here. Now we
do have runtime_cxxmodules, and we can actually properly add a
dependency here.
Without this patch a deleted C++ module file actually will never be regenerated.

This reverts commit 180cd90a.
It breaks lookup of functions with 'using ParentClass::Func'
in combination with modules which reuse the hidden flag for
module purposes.

See https://reviews.llvm.org/D37180 for a clang test case that
tests for regressions like this in the future.

In commit b8dbe76844923 we added signal.h to the modulemap to
fix a merging issue coming from sys/types.h. However, we include
this header directly in some other places so we can still encounter
this merging issue. This adds now the sys/types.h header also
to the modulemap to fix this once and for all.