[Patch] Fix the _GLIBCXX_ASSERT lossage

[Paolo Carlini]

Phil Edwards wrote:

>>Tested x86-linux,
>>
>How did you test it?  (I'm trying to come up with a list of things to always
>check when making testsuite changes.)
>
Eh! ;)

Actually, I have simply run the testsuite and then checked by inspection
from the log that -D_GLIBCXX_ASSERT had been always passed, in particular
for those testcases that had it missing before (i.e., collate/wchar_t)

Nothing particularly smart or "automatic", sorry. Luckily, in this case the
change is sufficiently straighforward ...

Paolo.