Comment 5 for bug 1091186

Sparc needs a custom lowlevellock.c on 32-bit sparc because
we have a situation where we don't know if we have the
proper atomic instructions available or not.

For example, if we don't have the v9 compare-and-swap available
we use spinlocks instead. And for futexes we use a special
24-bit atomic, which embeds the spinlock in the remaining
8-bits. That's what all of those atomic_compare_and_exchange_val_24_acq
etc. routines are all about.

I'll just add the necessary sparc32/libc-lowlevellock.c file
to fix this, thanks for the report.