Export of internal Abseil changes.

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22fceefcf070a0cf89bf1846bee16a9d36ad4161 by Derek Mauro <dmauro@google.com>:

Use function static for once initialization of flag registry.

This is a workaround for the MSVC debug constexpr initialization issue
in absl::once_flag.

GitHub #304

PiperOrigin-RevId: 248169007

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97bbe6a5233802b61e758c55f7ba8926539cc4ca by Chris Kennelly <ckennelly@google.com>:

Internal change

PiperOrigin-RevId: 248139347

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e72640ee079b9fa44e2c7f925fa0a608bcfea515 by Derek Mauro <dmauro@google.com>:

Re-write flags config. It doesn't have to be written in the convoluted
way it currently is in the opensource-only code path.

PiperOrigin-RevId: 248010502

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2a72552511b8086c78cb43012c1644e519b3807e by Abseil Team <absl-team@google.com>:

Handle pthread_getschedparam() failure.

Log an error message if pthread_getschedparam() fails.

In Android's Media Framework, libminijail (which I believe is a sandbox)
aborts the process if pthread_getschedparam() is called:

  media.swcodec: libminijail[7526]: blocked syscall: sched_getparam
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  /system/bin/tombstoned: received crash request for pid 7526

Although this CL cannot handle that extreme failure mode, it handles an
error return from pthread_getschedparam() and won't use the uninitialized
param.sched_priority value in that case.

PiperOrigin-RevId: 247999953

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bb154a92be37987d00d652c7c792594f2f515d83 by Abseil Team <absl-team@google.com>:

Allow intrinsic int128 to be set for __aarch64__ targets.

PiperOrigin-RevId: 247977594
GitOrigin-RevId: 22fceefcf070a0cf89bf1846bee16a9d36ad4161
Change-Id: I1f7ccfd82eb71446277a8e6f542fe835ac173d71