testsuite failures on v7 branch due to concept-checks

[Paolo Carlini]

Jonathan Wakely wrote:

>Sorry I didn't catch those earlier, I always test with concept-checks
>but haven't tested the v7 branch for a while.  Add -D_GLIBCXX_CONCEPT_CHECKS
>to scripts/testsuite_flags to reproduce this.
>  
>
Thanks Jonathan and please keep on testing the v7 branch on your machine
(with concept-checks enabled)

>I doubt I'll have time to analyze what's happening this week, sorry.
>  
>
Same here, of course, but I'm looking a bit into it today.

Paolo.