www/envoy: unbreak the port's build on i386 (at least)

Abseil developers say they don't know of anything faster than
CityHash32 for 32-bit x86 code, thus we must link this symbol
to unbreak the build:

ld: error: undefined symbol: absl::lts_20220623::
hash_internal::CityHash32(char const*, unsigned int)
>>> referenced by access_log_impl.cc