preadv2 is not supported on musl libc #3760
Description
The preadv2 function is present on -gnu target, however when compiling on -musl target, which is surprising.
The jobserver-rs would like to use it to optimize it's performance rust-lang/jobserver-rs#90 (the try_acquire optimization has shipped once but reverted, so I opened another PR to use raw syscall directly).
FYI, my motivation is to that this API is used in cc-rs to improve performance.