Justification: exec, execv etc are unix concepts and portable version
should be called differently.
Do no touch non-Zig code. Adjust error names as well, if associated.
Closes#5853.
Previously, updating the `SYS` enum for each architecture required
manually looking at the syscall tables and inserting any new additions.
This commit adds a tool, `generate_linux_syscalls.zig`, that automates
this process using the syscall tables in the Linux source tree. On
architectures without a table, it runs `zig cc` as a pre-processor to
extract the system-call numbers from the Linux headers.
