linux: fix potential event loop stall
linux: fix potential event loop stall

It was pointed out[0] that libuv could effectively enter an infinite
loop (but not a busy loop) under certain conditions when polling for
events:

1. When the architecture is 32 bits, and
2. When timeout > 0, i.e., finite, and
3. When timeout > max_safe_timeout (~30 minutes), and
4. When epoll_wait(timeout) returns 0, then
5. timeout was not properly updated on the next call to epoll_wait().

Inspection of the code uncovered a secondary bug where under a similar
set of circumstances the timeout could drift when the epoll_wait()
system call returned late.

[0] https://github.com/libuv/libuv/pull/354#discussion_r67837112

PR-URL: https://github.com/libuv/libuv/pull/922
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>

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