Auto merge of #116238 - tamird:gettimeofday, r=thomcc

time: use clock_gettime on macos

Replace `gettimeofday` with `clock_gettime(CLOCK_REALTIME)` on:

```
all(target_os = "macos", not(target_arch = "aarch64")),
    target_os = "ios",
    target_os = "watchos",
    target_os = "tvos"
))]
```

`gettimeofday` was first used in
time-rs/time@cc367ed
which predated the introduction of `clock_gettime` support in macOS
10.12 Sierra which became the minimum supported version in
58bbca958d917a89124da248735926f86c59a149.

Replace `mach_{absolute_time,timebase_info}` with
`clock_gettime(CLOCK_REALTIME)` on:

```
all(target_os = "macos", not(target_arch = "aarch64")),
    target_os = "ios",
    target_os = "watchos",
    target_os = "tvos"
))]
```

`mach_{absolute_time,timebase_info}` were first used in
time-rs/time@cc367ed
which predated the introduction of `clock_gettime` support in macOS
10.12 Sierra which became the minimum supported version in
58bbca958d917a89124da248735926f86c59a149.

Note that this change was made for aarch64 in
5008a317ce8e508c390ed12bff281f307313376e which predated 10.12 becoming
the minimum supported version. The discussion took place in
rust-lang/rust#91417 and in particular
rust-lang/rust#91417 (comment)
and
rust-lang/rust#91417 (comment)
are relevant.

Author: bors