Those functions aren't the real system calls provided by Linux, they're just glibc wrappers with added functionality. Linux kernel execve has absolutely no concept of PATH, it just opens the file at the provided pathname. That's a good thing too, user space might want to customize that stuff.
Yes. Shells typically do their own path resolution as well. I know GNU bash does, at least. I customized that logic in order to make a little library system for shell scripts.
