Funny clang behaviour

[Torbjörn Granlund]

We upgraded the FreeBSD GMP test systems from 11.2 to 11.3 and 12.0 to
12.1 and with those upgrades came clang 8.0.

We got some really novel failures when using clang++ for compiling GMP.
It spews out binary error messages which appears to be dumps of its own
RAM!  What clang actually thinks is wromg is anyone's guess.

I moved the failures to the "expected" failure section of
<https://gmplib.org/devel/tm/gmp/date.html>.

--
Torbjörn
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