emulators/qemu-user-static: fix build on main

Call sys_readlinkat() rather than the now removed readlinkeat().
Neither are public interfaces, but sys___readlinkat is somewhat more
so and is declared in libsys.h.

Reported by: cperciva
MFH: 2025Q1
Sponsored by: DARPA, AFRL

(cherry picked from commit 4afa6308d101da21a749701566c5088bc2c7041e)