Export of internal Abseil changes.

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5f1cf6547231f1b1daad6d1b785df6b0b999b3c9 by Samuel Benzaquen <sbenza@google.com>:

Fix uninitialized member in the `iterator` class by using a union of the two
possible states of the iterator.
This silences a Wuninitialized warning in gcc>=7.

PiperOrigin-RevId: 228175148

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98b4e3204c0ec3cfd4cb037e24d443ea4b63fc84 by CJ Johnson <johnsoncj@google.com>:

Factors out the implementation of InlinedVector::swap(...) into a private member function

PiperOrigin-RevId: 228173383

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f1432ad3a8b05285c6d55bc4754cfae765485b7f by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 227891984

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03fc00c7a4efc6000e6d9125cb2e252bffda76fe by Andy Getzendanner <durandal@google.com>:

Add a missing linebreak to a comment and markdownify two unordered lists.

PiperOrigin-RevId: 227861389

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0d66c9afba4fc9aa52e61d9fb410e165018a7b48 by Abseil Team <absl-team@google.com>:

Add an API to register a new source for the cycle clock.

PiperOrigin-RevId: 227779218

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14d3f9b70c8818b8541e5fb2f6ca4c59d479de31 by Andy Getzendanner <durandal@google.com>:

Correct a typo in a stripping marker.

PiperOrigin-RevId: 227750014

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59df88740f4e315beb57a8772f8bcf7879440c74 by Matt Kulukundis <kfm@google.com>:

Switch thread local handling to be more cross platform

PiperOrigin-RevId: 227695133

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75deed5bfcb5c42534e933f104aa7d94e11e348d by Abseil Team <absl-team@google.com>:

Rollback workaround toolchain bug for incorrect handling of thread_local in inline
functions

PiperOrigin-RevId: 227689133

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54994bf0afec026e6e0e7a199df0bbb4b7d9a4aa by Derek Mauro <dmauro@google.com>:

Add -pthread to linkopts where it actually belongs, on the library
that uses it.
Fixes https://github.com/abseil/abseil-cpp/issues/240.

PiperOrigin-RevId: 227612492

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893875f3536b7e0a1bad993aa6b2e083abb3b25a by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 227582833

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506c9b8e9002ca3389c7040473b68d4cbf94bdcc by Matt Kulukundis <kfm@google.com>:

Workaround toolchain bug for incorrect handling of thread_local in inline
functions

PiperOrigin-RevId: 227561449

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29ee90d96dfe3114cf93f9bb92ea0cc9e768a407 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 227054634
GitOrigin-RevId: 5f1cf6547231f1b1daad6d1b785df6b0b999b3c9
Change-Id: Ibc90566d92ee6e0ad7e150f513ec7f5d22ec0a94

1 files changed, 11 insertions, 1 deletions

diff --git a/absl/base/internal/cycleclock.cc b/absl/base/internal/cycleclock.cc
index a742df01f94a..9eb13b8cb8c0 100644
--- a/absl/base/internal/cycleclock.cc
+++ b/absl/base/internal/cycleclock.cc
@@ -22,6 +22,7 @@
 
 #include "absl/base/internal/cycleclock.h"
 
+#include <atomic>
 #include <chrono>  // NOLINT(build/c++11)
 
 #include "absl/base/internal/unscaledcycleclock.h"
@@ -52,17 +53,26 @@ static constexpr int32_t kShift = 2;
 #endif
 
 static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
+static std::atomic<CycleClockSourceFunc> cycle_clock_source;
 
 }  // namespace
 
 int64_t CycleClock::Now() {
-  return base_internal::UnscaledCycleClock::Now() >> kShift;
+  auto fn = cycle_clock_source.load(std::memory_order_relaxed);
+  if (fn == nullptr) {
+    return base_internal::UnscaledCycleClock::Now() >> kShift;
+  }
+  return fn() >> kShift;
 }
 
 double CycleClock::Frequency() {
   return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
 }
 
+void CycleClockSource::Register(CycleClockSourceFunc source) {
+  cycle_clock_source.store(source, std::memory_order_relaxed);
+}
+
 #else
 
 int64_t CycleClock::Now() {