Update webrtc's abseil-cpp

Copy external/abseil-cpp into webrtc to update to version 20211102.0
to pick up changes that fix compiling against musl libc.

Bug: 190084016
Test: m USE_HOST_MUSL=true host-native
Test: m checkbuild
Change-Id: I0ab600cd8db93a55eda8358cdbecd21c2f78d8fb

third_party/abseil-cpp/create_lts.py

@@ -0,0 +1,133 @@
+#!/usr/bin/env python3
+#
+# Copyright 2021 The Abseil Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""A script to do source transformations to create a new LTS release.
+
+   Usage: ./create_lts.py YYYYMMDD
+"""
+
+import sys
+
+
+def ReplaceStringsInFile(filename, replacement_dict):
+  """Performs textual replacements in a file.
+
+  Rewrites filename with the keys in replacement_dict replaced with
+  their values. This function assumes the file can fit in memory.
+
+  Args:
+    filename: the filename to perform the replacement on
+    replacement_dict: a dictionary of key strings to be replaced with their
+      values
+
+  Raises:
+    Exception: A failure occured
+  """
+  f = open(filename, 'r')
+  content = f.read()
+  f.close()
+
+  for key, value in replacement_dict.items():
+    original = content
+    content = content.replace(key, value)
+    if content == original:
+      raise Exception('Failed to find {} in {}'.format(key, filename))
+
+  f = open(filename, 'w')
+  f.write(content)
+  f.close()
+
+
+def StripContentBetweenTags(filename, strip_begin_tag, strip_end_tag):
+  """Strip contents from a file.
+
+  Rewrites filename with by removing all content between
+  strip_begin_tag and strip_end_tag, including the tags themselves.
+
+  Args:
+    filename: the filename to perform the replacement on
+    strip_begin_tag: the start of the content to be removed
+    strip_end_tag: the end of the content to be removed
+
+  Raises:
+    Exception: A failure occured
+  """
+  f = open(filename, 'r')
+  content = f.read()
+  f.close()
+
+  while True:
+    begin = content.find(strip_begin_tag)
+    if begin == -1:
+      break
+    end = content.find(strip_end_tag, begin + len(strip_begin_tag))
+    if end == -1:
+      raise Exception('{}: imbalanced strip begin ({}) and '
+                      'end ({}) tags'.format(filename, strip_begin_tag,
+                                             strip_end_tag))
+    content = content.replace(content[begin:end + len(strip_end_tag)], '')
+
+  f = open(filename, 'w')
+  f.write(content)
+  f.close()
+
+
+def main(argv):
+  if len(argv) != 2:
+    print('Usage: {} YYYYMMDD'.format(sys.argv[0], file=sys.stderr))
+    sys.exit(1)
+
+  datestamp = sys.argv[1]
+  if len(datestamp) != 8 or not datestamp.isdigit():
+    raise Exception(
+        'datestamp={} is not in the YYYYMMDD format'.format(datestamp))
+
+  # Replacement directives go here.
+  ReplaceStringsInFile(
+      'absl/base/config.h', {
+          '#undef ABSL_LTS_RELEASE_VERSION':
+              '#define ABSL_LTS_RELEASE_VERSION {}'.format(datestamp),
+          '#undef ABSL_LTS_RELEASE_PATCH_LEVEL':
+              '#define ABSL_LTS_RELEASE_PATCH_LEVEL 0'
+      })
+  ReplaceStringsInFile(
+      'absl/base/options.h', {
+          '#define ABSL_OPTION_USE_INLINE_NAMESPACE 0':
+              '#define ABSL_OPTION_USE_INLINE_NAMESPACE 1',
+          '#define ABSL_OPTION_INLINE_NAMESPACE_NAME head':
+              '#define ABSL_OPTION_INLINE_NAMESPACE_NAME lts_{}'.format(
+                  datestamp)
+      })
+  ReplaceStringsInFile(
+      'CMakeLists.txt', {
+          'project(absl LANGUAGES CXX)':
+              'project(absl LANGUAGES CXX VERSION {})'.format(datestamp)
+      })
+  # Set the SOVERSION to YYMM.0.0 - The first 0 means we only have ABI
+  # compatible changes, and the second 0 means we can increment it to
+  # mark changes as ABI-compatible, for patch releases.  Note that we
+  # only use the last two digits of the year and the month because the
+  # MacOS linker requires the first part of the SOVERSION to fit into
+  # 16 bits.
+  # https://www.sicpers.info/2013/03/how-to-version-a-mach-o-library/
+  ReplaceStringsInFile(
+      'CMake/AbseilHelpers.cmake',
+      {'SOVERSION 0': 'SOVERSION "{}.0.0"'.format(datestamp[2:6])})
+  StripContentBetweenTags('CMakeLists.txt', '# absl:lts-remove-begin',
+                          '# absl:lts-remove-end')
+
+
+if __name__ == '__main__':
+  main(sys.argv)