lib/: Use compound literals to avoid casts

lib/: Use compound literals to avoid casts

Casts are unsafe.

Compound literals also have the ability of converting values, but they
don't have the unwanted effects on safety --casts disable most useful
diagnostics--.

Compound literals are lvalues, which means their address can be taken,
and they can also be assigned to.  To avoid this, we force lvalue
conversion through a statement expression.

Signed-off-by: Alejandro Colomar <alx@kernel.org>