[0.12 backport] fix riscv64 build #1642

Job	Run time
prepare	2s
test / prepare	9m 37s
test / run (containerd, ./frontend/dockerfile, integration)	10m 2s
test / run (containerd, ./frontend/dockerfile, dockerfile)	11m 3s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	7m 21s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	8m 36s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	6m 51s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	11m 38s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	7m 14s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	10m 14s
test / run (oci, ./frontend/dockerfile, integration)	6m 45s
test / run (oci, ./frontend/dockerfile, dockerfile)	7m 41s
test / run (oci-rootless, ./frontend/dockerfile, integration)	7m 28s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	8m 57s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	6m 44s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	7m 55s
image (mainline)	7m 43s
image (labs)	9m 32s
release	0s
	2h 25m 23s

Provide feedback