Description:
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In ext/date/lib/fallbackmap.h you have:
        { "krat",  0,    7,  "Asia/Krasnoyarsk" },
        { "krast", 1,    8,  "Asia/Krasnoyarsk" },
        { "jst",   0,    9,  "Asia/Tokyo" },

but lots east Asia region do not use daylight saving time.
And in the test server if I use /usr/share/zoneinfo/Etc/GMT-8 as /etc/localtime, I'll get tm_isdat == 0 after a simple localtime_r call, which then resulting PHP think the timezone is UTC. (I removed date.timezone entry in php.ini since i want PHP using OS's timezone setting.)

Reproduce code:
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Remove date.timezone entry in php.ini and use /usr/share/zoneinfo/Etc/GMT-8 as /etc/localtime, then run date_default_timezone_get()

Expected result:
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Should return some timezone rest in GMT-8 region. (such as HongKong or Asia/Vientiane)

Actual result:
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Returns UTC