[Feature] Parallelism control

[kxxt]

Inspired by https://blog.quarticcat.com/posts/no-more-oom/ ,

I think tracexec is the perfect place to control the parallelism of build system. r8(it's not a linker anyway) really pushes my system near/to OOM when building AOSP based systems.

Define a group as a collection of filename patterns(plain text or regex). e.g. linker group with /ld and /ld.ldd. Then we can control how many processes can run at the same time by pausing excessive processes at execve syscall exit stop and continuing them once old processes exit.