Export of internal Abseil changes

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9beb68204986a015c9cb065b9fae4f9a8879a788 by Abseil Team <absl-team@google.com>:

Move Base64EscapeInternal and CalculateBase64EscapedLenInternal to an internal header.

PiperOrigin-RevId: 288917378

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90acfbe03b3f9f6de3ffa49c39343dfaa2c5d38c by Greg Falcon <gfalcon@google.com>:

Update macos CI script to support the ALTERNATE_OPTIONS environment variable.

PiperOrigin-RevId: 288913564

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f1572e870678cdcda6b48cb39780d1ad984e4c1b by Derek Mauro <dmauro@google.com>:

Makes absl::NullSafeStringView constexpr
Fixes https://github.com/abseil/abseil-cpp/issues/583

PiperOrigin-RevId: 288906940

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d28a8471e32c10caa64bfffe6d6d4d0a8d144013 by Abseil Team <absl-team@google.com>:

absl::GetFlag is lock free for small trivially copyable types.

PiperOrigin-RevId: 288768172

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2643b8ed1a1dc836b38ab9e46538a1af129ffd67 by Gennadiy Rozental <rogeeff@google.com>:

Eliminate call to callback from flag initialization.

We do not need to have this invocation inside FlagImpl::Init since SetCallback performs invocation anyways. Calling InitCallback from inside of Init complicates separation of value initialization from data guard initialization, which is about to happen.

PiperOrigin-RevId: 288732526

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22caa880b7a4cb6da34e16a2e064a473c99e880b by Abseil Team <absl-team@google.com>:

Fix the documentation on how to create a null string_view.

PiperOrigin-RevId: 288727968

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10727c5cadc561837141176f4c9b9717cec9233a by Greg Falcon <gfalcon@google.com>:

Change CI scripts for gcc to use the ALTERNATE_OPTIONS file as well.

PiperOrigin-RevId: 288718855

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5d1e2dd6c7fb12af8aa4337a0f61872f5f0c5992 by Greg Falcon <gfalcon@google.com>:

Add an option for using inline namespaces in Abseil.

PiperOrigin-RevId: 288614491
GitOrigin-RevId: 9beb68204986a015c9cb065b9fae4f9a8879a788
Change-Id: If9acd46301e3df8cb231b4c16f7ed651bf4fb3c3

ci/macos_xcode_bazel.sh

@@ -41,6 +41,10 @@ echo "---------------"
 
 cd ${ABSEIL_ROOT}
 
+if [ -n "${ALTERNATE_OPTIONS:-}" ]; then
+  cp ${ALTERNATE_OPTIONS:-} absl/base/options.h || exit 1
+fi
+
 ${BAZEL_BIN} test ... \
   --copt=-Werror \
   --keep_going \