Export of internal Abseil changes.

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4e043a11b4c10a24e84046827ee16f47e11e35cc by Abseil Team <absl-team@google.com>:

Merge of https://github.com/abseil/abseil-cpp/pull/136

PiperOrigin-RevId: 218197648

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e61f06e1e601061a443feaa8c5207c52437bd641 by Abseil Team <absl-team@google.com>:

Don't include <iostream> into int128, it's wasteful

Including iostream emits a global constructor for initializing std::cout and
friends, which isn't actually used by this file.

PiperOrigin-RevId: 218156386

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8a6c82396e4c956be7f285328aec131cb4965f16 by Xiaoyi Zhang <zhangxy@google.com>:

Fix MSVC compiler warnings on discarding return values of functions with 'nodiscard'
attribute.

PiperOrigin-RevId: 217883401

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abf3e3a0f22bc4070df9dbc9a4ef4d883ed686bf by Tom Manshreck <shreck@google.com>:

Update public README to add new libraries

PiperOrigin-RevId: 217879399

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43b3b420a4e861711abbfbd497b8f2b3de17ec8c by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 217780963

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1c8831947ca6a65a63842e6bd5f37a7c102a4e1b by Abseil Team <absl-team@google.com>:

Fix typo in a comment (missing comma in usage example).

PiperOrigin-RevId: 217776645
GitOrigin-RevId: 4e043a11b4c10a24e84046827ee16f47e11e35cc
Change-Id: I8999ae928da7a0030b4ecfd8d13da8522fdd013a