Export of internal Abseil changes.

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f9f068aa8a260dc576398e47b8e4540902e41358 by Derek Mauro <dmauro@google.com>:

Fix test string with embedded NUL. Currently parses as octal.

PiperOrigin-RevId: 237088193

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d271ffdd3f450f817f6d30e98ff39d439aaf3a98 by Abseil Team <absl-team@google.com>:

Make symbolizer examine any mapping with read+exec permission regardless of 'w' bit.

PiperOrigin-RevId: 237056461

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af315f8306d36a7367a452fd0b58cafdbf20719d by Abseil Team <absl-team@google.com>:

Switch comments referencing base:: CondVar and Mutex to absl::.

PiperOrigin-RevId: 236917884

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c624d5d1c0bdb917bff5e651ba40599472f84e0e by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 236898300

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3cdc82429af964846d1152f49148abc61d196a4b by Samuel Benzaquen <sbenza@google.com>:

Make the `long double` overload if AbslHashValue a template to avoid invalid
conversions with implicit operators.

This overload was never meant to capture anything other than `long double` and any current caller to it that wasn't a `long double` is potentially a bug.
In particular, any type with an implicit `bool` conversion is calling this
overload instead of trying to find a hash<> specialization, thus causing
pretty bad hash behavior.

PiperOrigin-RevId: 236877073
GitOrigin-RevId: f9f068aa8a260dc576398e47b8e4540902e41358
Change-Id: If9cc008dd814f0ca06ed881f612c06575f1f7137