Upcoming WASI snapshots omit the `PROCESS_CPUTIME` clock, since WASI has
no inherent concept of processes, and since implementations which don't
use a process for each instance don't have a way to implement it
efficiently.
However, `clock`, `times`, and `getrusage` are useful functions, so
provide optional emulated version of them, using the `MONOTONIC` clock.
This means these implementations will measure not just the program's
own CPU time, but also time spent suspended while other programs are
running.
Due to this difference in behavior, put these implementations behind
a flag. Users must pass `-D_WASI_EMULATED_PROCESS_CLOCK` and link with
`-lwasi-emulated-process-clocks` to enable them.
See the WHATSNEW file for details. The biggest change in musl is the
switch to 64-bit time_t for 32-bit targets, however WASI libc was already
using 64-bit time_t. The main change affecting WASI is an update to
Unicode 12.1.0.
Add at least a one-line comment on every
`#ifdef __wasilibc_unmodified_upstream` briefly indicating what its
purpose is.
While here, reenable some of the code that was previously disabled when
getenv wasn't supported, as getenv is now supported.
