pthread_spin_t variable (4 bytes) but telling read that they were
reading sizeof(struct pthread_spinlock_st) (12 bytes). This led to
overwriting other things on the stack, like the return address. Oops.
Fix by changing READ call here (and elsewhere, for future safety) to:
READ(,, &variable, sizeof(variable))
instead of
READ(,, &variable, sizeof(type)).
Fixes a crash in gdb when running "thread examine all" reported by
Bill Studenmund.
