The double-double precision can be really large.

I don't know where I had pulled the earlier smaller limit,
but sisyphus@ set me right.
Skip the test if in linux but not in x86*.

The state of things found by Ævar in ppc linux was even weirder:
most -- but not all! -- text symbols were in D section, not in T.

Skipping is fine since we are here after best-effort testing,
failing softly is quite acceptable.