build: specify c-compiler for c-ares
build: specify c-compiler for c-ares

so we can test the build in a clang-only environment.

Signed-off-by: Kefu Chai <cdc92d111bae0ed1ee3b3c8a1f849fcffc6b44f7@gmail.com>

cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,cloudius-systems/seastar,avikivity/seastar,scylladb/seastar,dreamsxin/seastar,syuu1228/seastar,avikivity/seastar,cloudius-systems/seastar,scylladb/seastar,syuu1228/seastar,dreamsxin/seastar,dreamsxin/seastar,syuu1228/seastar