lib: Implement pthread_cancel via pthread_kill on Android

[SeTSeR]

Android NDK does not provide pthread_cancel method, see discussion here, for example. This PR proposes simple workaround for this, initially proposed by @Hax4us. This change is fairly trivial so I don't expect any licensing or other issues. Official documentation of Android NDK states that correct implementation of pthread_cancel is too difficult, so we should consider to use something else on Android instead. Proper solution probably should use conditional variables.

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[SeTSeR]

Failing tests under sanitizer don’t seem to be connected with this change, as behavior for platforms, another then Android, did not change at all.

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