Commit 4e2ab71dfe reverts
micropython/micropython@5cf71b5596
which solved micropython/micropython#6046, which I'm seeing again on my
gentoo system with D_FORTIFY_HARDENED enabled by default.
Unfortunately we can't just revert the revertion because circuitpython
enforces prototypes for defined functions, which is why 4e2ab71d was
implemented initially. Micropython doesn't suffer from this issue.
The implemented fix is to just circumvent D_FORTIFY_SOURCE, a nice
side-effect is we can remove the re-implemented functions that were
added on the initial `string.h` removal.
50e24c31ed