Export of internal Abseil changes

--
c99f979ad34f155fbeeea69b88bdc7458d89a21c by Derek Mauro <dmauro@google.com>:

Remove a floating point division by zero test.

This isn't testing behavior related to the library, and MSVC warns
about it in opt mode.

PiperOrigin-RevId: 285220804

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68b015491f0dbf1ab547994673281abd1f34cd4b by Gennadiy Rozental <rogeeff@google.com>:

This CL introduces following changes to the class FlagImpl:
* We eliminate the CommandLineFlagLocks struct. Instead callback guard and callback function are combined into a single CallbackData struct, while primary data lock is stored separately.
* CallbackData member of class FlagImpl is initially set to be nullptr and is only allocated and initialized when a flag's callback is being set. For most flags we do not pay for the extra space and extra absl::Mutex now.
* Primary data guard is stored in data_guard_ data member. This is a properly aligned character buffer of necessary size. During initialization of the flag we construct absl::Mutex in this space using placement new call.
* We now avoid extra value copy after successful attempt to parse value out of string. Instead we swap flag's current value with tentative value we just produced.

PiperOrigin-RevId: 285132636

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ed45d118fb818969eb13094cf7827c885dfc562c by Tom Manshreck <shreck@google.com>:

Change null-term* (and nul-term*) to NUL-term* in comments

PiperOrigin-RevId: 285036610

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729619017944db895ce8d6d29c1995aa2e5628a5 by Derek Mauro <dmauro@google.com>:

Use the Posix implementation of thread identity on MinGW.
Some versions of MinGW suffer from thread_local bugs.

PiperOrigin-RevId: 285022920

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39a25493503c76885bc3254c28f66a251c5b5bb0 by Greg Falcon <gfalcon@google.com>:

Implementation detail change.

Add further ABSL_NAMESPACE_BEGIN and _END annotation macros to files in Abseil.

PiperOrigin-RevId: 285012012
GitOrigin-RevId: c99f979ad34f155fbeeea69b88bdc7458d89a21c
Change-Id: I4c85d3704e45d11a9ac50d562f39640a6adbedc1

1 files changed, 4 insertions, 0 deletions

diff --git a/absl/types/optional.h b/absl/types/optional.h
index 14032598d9b0..2025e29f86a9 100644
--- a/absl/types/optional.h
+++ b/absl/types/optional.h
@@ -43,11 +43,13 @@
 #include <optional>  // IWYU pragma: export
 
 namespace absl {
+ABSL_NAMESPACE_BEGIN
 using std::bad_optional_access;
 using std::optional;
 using std::make_optional;
 using std::nullopt_t;
 using std::nullopt;
+ABSL_NAMESPACE_END
 }  // namespace absl
 
 #else  // ABSL_USES_STD_OPTIONAL
@@ -65,6 +67,7 @@ using std::nullopt;
 #include "absl/types/internal/optional.h"
 
 namespace absl {
+ABSL_NAMESPACE_BEGIN
 
 // nullopt_t
 //
@@ -754,6 +757,7 @@ constexpr auto operator>=(const U& v, const optional<T>& x)
   return static_cast<bool>(x) ? static_cast<bool>(v >= *x) : true;
 }
 
+ABSL_NAMESPACE_END
 }  // namespace absl
 
 namespace std {