add per-syscall grates

[drapl0n]

• adds geteuid, getuid, getpid, and close grate

[stupendoussuperpowers]

geteuid already exists right?

Also, can these just be replaced by using the testing-grate? Instead of needing to have individual grates for all of these single syscalls?

[Yaxuan-w]

Can we auto-generate these grates?

[stupendoussuperpowers]

Can we auto-generate these grates?

Agree to this, or like I pointed out in my comment -
the testing-grate can be configured for these use cases I think since it just takes runtime arguments and maps those with the return values we need.

[rennergade]

We can just not merge this branch. I think it's useful to have for now since these are used for the policy graph

[stupendoussuperpowers]

I think it's useful to have for now since these are used for the policy graph

In that case I am not opposed to merging these.

Few things:

1. Maybe we can change the folder name from "per-syscall-grates" to "single-syscall-grates" or "passthrough-syscall-grates" or something clearer/better worded.

2. build.conf files are not needed anymore so we can remove them.

3. All of these grates just pass the syscall through without any logging/parameter modifications, not sure if we should be doing at least something here. If these are being used for benchmarking, it might be a little unrepresentative of what a typical single-syscall grate is used for.