Switch Instant to use CLOCK_BOOTTIME on Android.

[jfgoog]

This is a long-term patch we have carried for the Android platform:

https://android.googlesource.com/toolchain/android_rust/+/refs/heads/main/patches/longterm/rustc-0018-Switch-Instant-to-use-CLOCK_BOOTTIME.patch

[rustbot]

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[the8472]

Near-duplicate of #132331 (esp. #132331 (comment))
See also:

• Switch Instant to use CLOCK_BOOTTIME #87907
• use CLOCK_BOOTTIME in Instant::now #88714
• Instant::duration_since returns a shortened duration if a suspend occurred #87906

And personally I think android shouldn't be carrying this patch, since it indicates you have broken code somewhere else that relies on explicitly disclaimed behavior.

[tgross35]

Closing because as @the8472 mentioned, this was discussed in #132331 (comment) and the plan is to introduce an alternative clock that has the needed guarantees.