mysql57 and i386

[Greg Troxel <gdt%lexort.com@localhost>]

In the 2018Q3 bulk builds, mysql57 seems to be failing on i386, even on
-8.   And it fails with head pkgsrc on netbsd-8.   It seems to have
something to do with atomics:

/usr/ANONCVS/pkgsrc/databases/mysql57-client/work/mysql-5.7.23/include/my_atomic.h:65:4: error: #error Native atomics support not found!

and I suspect that's because we are building for 486 whereas people in
the Linux world are building for a higher instruction set.

So I wonder if we should be adding some cpu tuning for this package in
particular, even though then the resulting package won't work on an
actual 486 (or amd geode?).  But that seems better, even if a bit
mysterious, than not getting a package at all for modern i386 machines.

Are others seeing this?  Thoughts?  Other ideas?