CMake build in Linux links libcurl to libdl

[reddwarf69]

The only use of dlopen seems to be in packages/vms/report_openssl_version.c. But in my Linux builds -ldl ends up in the CURL_LIBS variable, so:

• libcurl.so links to it
• it's included in the .pc file
• it's in CURL::libcurl's INTERFACE_LINK_LIBRARIES

[bagder]

some OpenSSL versions back in the day needed libdl, that's probably why

[reddwarf69]

FWIW I am personally using https://github.com/RedDwarf69/curl/tree/cmake. I'm not creating PRs because I have not tried to make it ready for that (e.g I'm increasing the minimum required cmake version... and I have no idea how much you want to keep cmake 3.2 support).
I'm solving this with reddwarf69@cb4a72c