Export of internal Abseil changes

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1d8539bec6f0b390360b896d4c43da5b546486e1 by Derek Mauro <dmauro@google.com>:

Load C++ BUILD rules from the @rules_cc repository.
Required for Bazel 1.0.

Internal import of GitHub Pull Request #351

PiperOrigin-RevId: 263768433

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017d315f1b5d4b4f2e1d6615265134f1001f2b84 by Derek Mauro <dmauro@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 263762409

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77b3cdeca653df595d4709db74230f38b35c9c7c by CJ Johnson <johnsoncj@google.com>:

Fixes logical error in test file's static_assert

PiperOrigin-RevId: 263610500

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cd358e4efc21c8c2ef79cb137d75c829aeee4417 by Derek Mauro <dmauro@google.com>:

Remove bazel_toolchains from WORKSPACE.bazel

The Abseil build doesn't use it anymore.

PiperOrigin-RevId: 263609624
GitOrigin-RevId: 1d8539bec6f0b390360b896d4c43da5b546486e1
Change-Id: I17a5ddfe7409aa110b945aeda4de14bc217907ad