Title: curl is compiled without c-ares support and is prone to crashes on DNS timeouts due to longjmp.

Description: curl dependency (via cmake_external) was added as part of #5387 but does not use the already existing c-ares library for async DNS resolution and is prone to crashes on modern Linux kernels.

Suggested fix:

[Moved to a separate issue, irrelevant] change curl from cmake_external to Bazel-native with a manually written BUILD file like https://github.com/tensorflow/tensorflow/blob/master/third_party/curl.BUILD

• Add deps = [//external:ares, //external:zlib] and -DUSE_ARES, -DHAVE_ZLIB_H options

This will use Envoy's c-ares and zlib dependencies and instruct curl to use c-ares for DNS resolutions.