The ornamental design for a toybuildingblock, as shown and described.
FIG. 1 is a front perspective view of a toy building block embodying the new design;
FIG. 2 is a rear perspective view thereof;
FIG. 3 is a front plan view thereof;
FIG. 4 is a rear plan view thereof;
FIG. 5 is a left side view thereof;
FIG. 6 is a right side view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
FIGS. 1-8 show features of a toy building block in broken lines. The broken lines in FIGS. 1-8 are included for the purpose of illustrating portions of the toy building block which form no part of the claimed design.