libc/env: Migrate to upstream musl

Migrate all identical files under libc/env to upstream musl.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
libc/stdlib: Migrate to upstream musl

Migrate all identical files under libc/stdlib to upstream musl.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>