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/absl/debugging/symbolize_emscripten.inc

@@ -0,0 +1,72 @@
+// Copyright 2020 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.
+
+#include <cxxabi.h>
+#include <emscripten.h>
+
+#include <algorithm>
+#include <cstring>
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/debugging/internal/demangle.h"
+#include "absl/strings/numbers.h"
+#include "absl/strings/str_cat.h"
+#include "absl/strings/string_view.h"
+
+extern "C" {
+const char* emscripten_pc_get_function(const void* pc);
+}
+
+// clang-format off
+EM_JS(bool, HaveOffsetConverter, (),
+      { return typeof wasmOffsetConverter !== 'undefined'; });
+// clang-format on
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+void InitializeSymbolizer(const char*) {
+  if (!HaveOffsetConverter()) {
+    ABSL_RAW_LOG(INFO,
+                 "Symbolization unavailable. Rebuild with -sWASM=1 "
+                 "and -sUSE_OFFSET_CONVERTER=1.");
+  }
+}
+
+bool Symbolize(const void* pc, char* out, int out_size) {
+  // Check if we have the offset converter necessary for pc_get_function.
+  // Without it, the program will abort().
+  if (!HaveOffsetConverter()) {
+    return false;
+  }
+  const char* func_name = emscripten_pc_get_function(pc);
+  if (func_name == nullptr) {
+    return false;
+  }
+
+  strncpy(out, func_name, out_size);
+
+  if (out[out_size - 1] != '\0') {
+    // strncpy() does not '\0' terminate when it truncates.
+    static constexpr char kEllipsis[] = "...";
+    int ellipsis_size = std::min<int>(sizeof(kEllipsis) - 1, out_size - 1);
+    memcpy(out + out_size - ellipsis_size - 1, kEllipsis, ellipsis_size);
+    out[out_size - 1] = '\0';
+  }
+
+  return true;
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl