The ornamental design for a toybuildingblock, as shown and described.
FIG. 1 is a perspective view of a toy building block embodying the new design;
FIG. 2 is a front side view thereof, the back side view being a mirror image thereof;
FIG. 3 is a right side view thereof, the left side view being a mirror image thereof; and,
FIG. 4 is a top plan view thereof, the bottom plan view being a mirror image thereof.
FIGS. 1-4 show features of a toy building block in broken lines. The broken lines in FIGS. 1-4 are included for the purpose of illustrating portions of the toy building block which form no part of the claimed design.