Export of internal Abseil changes.

--
5f1ab09522226336830d9ea6ef7276d37f536ac5 by Abseil Team <absl-team@google.com>:

Clarify the documentation of ABSL_MUST_USE_RESULT.

PiperOrigin-RevId: 221663609

--
af4c8359a20d56369fd1dce318220cf3be03ca66 by Greg Falcon <gfalcon@google.com>:

Internal change

PiperOrigin-RevId: 221538448

--
487cd09bd1942bf607080deeae38fee6ce66f294 by Eric Fiselier <ericwf@google.com>:

Work around emscripten bugs and missing features in absl/time:time_test.

The emscripten toolchain has a couple of issues that cause time_test
to fail. Specifically:

1) emscripten doesn't support signals.
2) The javascript implementation of strftime/strptime use different expansions
of '%c' that mean it doesn't round-trip.

PiperOrigin-RevId: 221523701

--
5823652e6a200b97b07334bc47128dfac40e20fc by Xiaoyi Zhang <zhangxy@google.com>:

Fix MSVC compiler warning by explicitly casting to char.
Currently our MSVC build breaks with the following error:
raw_hash_set.h(406): warning C4309: 'argument': truncation of constant value

PiperOrigin-RevId: 221492585

--
c5806358320711a5efbe5c523df13e14ab53a17d by Greg Falcon <gfalcon@google.com>:

Replace calls to getpagesize() with the more portable sysconf(_SC_PAGESIZE); the latter is in POSIX 1.0 and is called out in the Linux `getpagesize` man page as a more portable spelling.

PiperOrigin-RevId: 221492471

--
19ffe82851072229bb7ce73f754ffe4c18e8c575 by Abseil Team <absl-team@google.com>:

Fix -Wundef error in absl/hash/internal/hash.h.

PiperOrigin-RevId: 221444120

--
b30f3d0a848563b6e4ec33f3dc085831dfabb748 by Jon Cohen <cohenjon@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 221339736
GitOrigin-RevId: 5f1ab09522226336830d9ea6ef7276d37f536ac5
Change-Id: I96223d522d98bf6616dea88eb047c2d536eeddd0

absl/container/internal/raw_hash_set.h

@@ -403,7 +403,7 @@ struct GroupSse2Impl {
   }
 
   void ConvertSpecialToEmptyAndFullToDeleted(ctrl_t* dst) const {
-    auto msbs = _mm_set1_epi8(0x80);
+    auto msbs = _mm_set1_epi8(static_cast<char>(-128));
     auto x126 = _mm_set1_epi8(126);
 #if SWISSTABLE_HAVE_SSSE3
     auto res = _mm_or_si128(_mm_shuffle_epi8(x126, ctrl), msbs);