compiletest/raise_fd_limit: use libc instead of custom impl
compiletest/raise_fd_limit: use libc instead of custom impl

Fixes #29751.

graydon/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust