Ensure all curl symbols are exported

In the recent update of libcurl (2.5.0-278-g807c7fa58) its layout has
changed: private function `Curl_version_init()` which used to fill-in
info structure was eliminated. As a result, no symbols for
`libcurl_la-version.o` remained used, so it wasn't included in tarantool
binary. And `curl_version` and `curl_version_info` symbols went missing.

According to libcurl naming conventions all exported symbols are named
as `curl_*`. This patch lists them all explicitly in `exprots.h` and
adds the test.

Close #5223