Gcc builtin review: strpbrk, strspn, strcspn

[Ondřej Bílka]

These do relatively good job.

These would be typical use-case for ufuncs. In most use cases accept
argument is consant so you want to precompute it as array as one
implementation computes table with characters and then checks if each
character is in table.

But on x64 there is better implementation which is only case where
sse4.2 instructions are useful in glibc string function.

So you need to do resolving if to expand table based on if cpu uses
sse4.2 which gcc cannot do.