Add support for string helper functions

[dthaler]

Describe the feature you'd like supported

Linux supports:

• bpf_strncmp
• bpf_strtoul
• bpf_strtol

Proposed solution

Add support for the same Linux APIs

Additional context

See also PR #3719 from @ben-zen

[ben-zen]

@shankarseal I'm happy to take this task on, I can't assign it to myself as is though.