bug#32773: [PATCH] Fix clang libstdc++ header location search

[Carl Dong]

Hi David!

This patch is most welcome, I’m wondering if you think it’d be possible to add 
more details in the comments for future readers of the code. See below.

> On Nov 13, 2019, at 11:56 AM, David Truby <address@hidden> wrote:
> 
> +                            ;; Make clang look for libstdc++ in the right 
> location
> +                            (("LibStdCXXIncludePathCandidates\\[\\] = \\{")
> +                             (string-append 
> "LibStdCXXIncludePathCandidates[] = { \"" gcc "/include/c++\","))
I believe the reason why clang’s “auto detection” fails here is because it 
expects the /include dir containing c++ to be under the same directory as 
LibDir, correct? Perhaps we can note that since in Guix, we put the libs in a 
separate output, we invalidate the aforementioned expectation, and this is why 
we need to manually add this path.

Another point: Perhaps we can add the path on a separate line instead of it 
being on the same line?

Otherwise, looks great!

Cheers,
Carl Dong