deps: fix building with system c-ares on Linux

The change in nodejs#39724 breaks building with system c-ares
(`--shared-cares`):
```
In file included from ../src/cares_wrap.cc:25:
../src/cares_wrap.h:25:11: fatal error: ares_nameser.h: No such file or
directory
   25 | # include <ares_nameser.h>
      |           ^~~~~~~~~~~~~~~~
```

Since `ares_nameser.h` isn't available with a default system c-ares
installation, let's copy it as our private header here.

Tested to build fine on Arch Linux with shared c-ares.