Problem

The #35 merge cleared the wide-character blocker; the libc++ build then failed with two platform-detection errors:

chrono.cpp: error: "Monotonic clock not implemented on this platform"
__locale:   error: unknown rune table for this platform -- do you mean to define _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE?

Both are because libc++ doesn't recognize Nanvix as a platform.

Fix (add Nanvix platform support to libc++)

• chrono.cpp — Nanvix provides clock_gettime() + CLOCK_MONOTONIC (declared in <time.h>, defined in libc.a), so add __nanvix__ to the targets that define _LIBCPP_HAS_CLOCK_GETTIME (alongside OpenBSD/hurd). steady_clock then uses clock_gettime(CLOCK_MONOTONIC). (The libc's <unistd.h> doesn't advertise _POSIX_TIMERS, which is why the generic detection missed it — fixing that upstream would also work.)
• __config + __cxx03/__config — Nanvix has no platform ctype "rune table", so use libc++'s built-in default table by adding __nanvix__ to the _LIBCPP_PROVIDES_DEFAULT_RUNE_TABLE list (as NuttX/Fuchsia/wasi do). The locale base API then falls through to the BSD POSIX fallbacks.

This keeps localization enabled (<locale>, <iostream>, <regex>) rather than disabling it — consistent with the fork's existing __nanvix__ handling already present in __config.

Caveat

Iterative stage-1 bring-up. These clear the two detection errors; subsequent libc++/libc++abi compile or link issues may surface next. Validated on merge (PR CI verifies stage 0 only).