[v3] debug mode

[Rainer Orth]

Benjamin Kosnik writes:

> Try this.

This did it, thanks.  make check-g++ completed successfully, and make check
for libstdc++-v3, while still running, looks good either.

I'll post another patch necessary to get at least alpha-dec-osf4.0f back to
bootstrap land (due to another, unrelated issue) as soon as the tests have
completed.

	Rainer

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Rainer Orth, Faculty of Technology, Bielefeld University