Allow ROOT_INCLUDE to specify standard library include paths

[Y--]

This way we do not need g++ at runtime

[Axel-Naumann]

We try to layer ROOT on top of cling, as cleanly as possible. Thus cling should use ROOT_INCLUDE. Can we maybe adjust the interpreter construction instead, passing -isystem and -nostdinc++? Then cling could skip the stdinc++ determination, reacting on -nostdinc++ being passed as an argument.

[Y--]

That would be great and makes much more sense indeed.
Is it something that is already implemented or does it need to be?

[Axel-Naumann]

Handling of -isystem should exist; skipping the gcc invocation if -nostdinc++ is passed or the ROOT part of the compiler includes do not exist.

[Y--]

It works properly indeed.
Here is the new version : Y--@39736e1

[Axel-Naumann]

Thank you for your PR! Nice ideas, let's get this in! Please let me know if one of my comments wasn't precise enough or misunderstood your patch.

[Y--]

Thanks for your quick review!
I'll try to work on your suggestions asap so you can integrate them.
Also, do you want me to do the same PR on Cling project?

[Axel-Naumann]

@Y-- - no need for an extra PR for cling! We will apply the changes from ROOT's cling to the cling repo.

[Axel-Naumann]

@Y-- Indeed, last of -O3 -O0 wins.

[Axel-Naumann]

Where's this needed?

[Y--]

Oups, I forgot to remove that. It's not used indeed.
Removed here : Y--@83e6fc7

[Axel-Naumann]

Excellent! Merged as 10cf52d..73b3a1d into master. (I have squashed some of your commits.)

Thank you for your contributions!

[Y--]

Awesome! Thank you so much :-)