x/vulndb: failure to build on aix/ppc64

[mknyszek]

https://build.golang.org/log/be5dbd3c54de7c236cf6114f0894ccfc71961aa4

Possibly related to #58301.

[mknyszek]

(Just noting this down for a comment in some x/build code. I don't mean to imply this necessarily should work. Feel free to close.)