Do libc++, or libc++abi, or LLVM issue syscalls directly?

Hi!

I'm in an embedded scenario in which I need to take care of what
syscalls are issued and from where. I'm wondering if libc++/libc++abi
(or even code generated from LLVM) can issue syscalls directly, or if
their access to system resources is always done via libc or via other
libraries.

In case you issue syscalls directly, is that centralized in some
source files? I searched for it in the code but couldn't find any
invocation of system calls...

Kind regards and thanks a lot,

ardi