[committed] hppa: Drop 16-byte pthread lock alignment

[Sam James]

Florian Weimer <fw@deneb.enyo.de> writes:

> * John David Anglin:
>
>> hppa: Drop 16-byte pthread lock alignment
>>
>> Linux threads were removed about 12 years ago and the current
>> nptl implementation only requires 4-byte alignment for pthread
>> locks.
>>
>> The 16-byte alignment causes various issues. For example in
>> building ignition-msgs, we have:
>>
>> /usr/include/google/protobuf/map.h:124:37: error: static assertion failed
>>   124 |   static_assert(alignof(value_type) <= 8, "");
>>       |                 ~~~~~~~~~~~~~~~~~~~~^~~~
>>
>> This is caused by the 16-byte pthread lock alignment.
>
> This was done deliberately to preserve ABI.  This change needs a mass
> rebuild because struct offsets after pthread_mutex_t members are
> likely to change.

On HPPA, I think we _may_ be fine with ABI breaks, but of course
we should use the proper mechanisms for that if we're doing it to
advertise it fully and allow distributions and users to prepare.

(We've done them before and there's not really any cache of binaries
that we need to keep compat. with anyway, it's more important to keep
things building usually.)

thanks,
sam
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