score: Use unsigned long for atomic integers

Use unsigned long instead of uint_fast32_t since C11 provides only a
ATOMIC_LONG_LOCK_FREE macro constant.  This makes it also possible to
use properly typed integer literals like 123UL.  It is now clear which
compatible type should be used for the atomic integer.
score: Use void * for some atomic pointer ops
smptests/smpatomic08: Add initialization test case