Export of internal Abseil changes

--
93dd18f415e54697965c56760612b4ff6c9d15d2 by Derek Mauro <dmauro@google.com>:

Implement Bazel's --distdir flag avoid a dependency on GitHub being up.
Move the Docker container identifiers to a common file.

PiperOrigin-RevId: 302045549

--
7b462d31139e3153462cd20ae63b161ac749e839 by Derek Mauro <dmauro@google.com>:

Fix an unused variable warning in optional.h

PiperOrigin-RevId: 301810782

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6b533ba9170eed065aec69e48ebab3279fcb3e09 by Abseil Team <absl-team@google.com>:

Disable ASan and MSan instrumentation for AArch64 stack unwind functions. They read random locations on the stack and might step on sanitizer's redzones.

PiperOrigin-RevId: 301674204
GitOrigin-RevId: 93dd18f415e54697965c56760612b4ff6c9d15d2
Change-Id: I2d84d66b054f90b851fb3a968679f112dfe84636

ci/linux_gcc-latest_libstdcxx_cmake.sh

@@ -34,6 +34,9 @@ if [ -z ${ABSL_CMAKE_BUILD_TYPES:-} ]; then
   ABSL_CMAKE_BUILD_TYPES="Debug Release"
 fi
 
+source "${ABSEIL_ROOT}/ci/linux_docker_containers.sh"
+readonly DOCKER_CONTAINER=${LINUX_GCC_LATEST_CONTAINER}
+
 for std in ${ABSL_CMAKE_CXX_STANDARDS}; do
   for compilation_mode in ${ABSL_CMAKE_BUILD_TYPES}; do
     echo "--------------------------------------------------------------------"
@@ -47,7 +50,7 @@ for std in ${ABSL_CMAKE_CXX_STANDARDS}; do
       --rm \
       -e CFLAGS="-Werror" \
       -e CXXFLAGS="-Werror" \
-      gcr.io/google.com/absl-177019/linux_gcc-latest:20200106 \
+      ${DOCKER_CONTAINER} \
       /bin/bash -c "
         cd /buildfs && \
         cmake /abseil-cpp \