CLEANUP: tree-wide: reorder a few structures to plug some holes around locks

CLEANUP: tree-wide: reorder a few structures to plug some holes around locks

A few structures were slightly rearranged in order to plug some holes
left around the locks. Sizes ranging from 8 to 32 bytes could be saved
depending on the structures. No performance difference was noticed (none
was expected there), though memory usage might be slightly reduced in
some rare cases.