This just happened to break the Windows build because of the
`GetObject` macro in `windows.h`, so I added a kludge to
PollResultGeneric.hxx.

Relax the assertions.  This is necessary if BlockingCall() is used
before the thread is started.

The former was deprecated with C++14.

According to the C++11 and C++17 standards, both files are identical.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This replaces the old `dead` flag which was unreliable; it was `false`
if the EventThread was not yet started, which could cause deadlocks in
BlockingCall().

Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Fixes thread sanitizer warnings.

Fixes thread sanitizer warnings.

Move its code to DeferEvent instead.

The intrusive contains can easily erase items without searching
through the whole list.  This removes a good amount of runtime
overhead.

By using an "intrusive" data structure, we can easily eliminate
struct TimerRecord.

Prepare to eliminate the TimerRecord struct.

Allows eliminating lots of complexity and workarounds for bogus
assertion failures.

Fixes build breakage by commit 4e5271fc; and this method does make
sense in non-debug builds.