For the commandline tool, we expect to be passed
SSL_CONN_CONFIG(CAfile); for library use, the use should pass a set of
trusted roots (like in other TLS backends).
This also removes a dependency on Security.framework when building on
macOS.
Closes#7250
Previously compiling rustls on Mac would only complete if you also
compiled the SecureTransport TLS backend, which curl would prefer to
the Rust backend.
Appending these flags to LDFLAGS makes it possible to compile the
Rustls backend on Mac without the SecureTransport backend, which means
this patch will make it possible for Mac users to use the Rustls
backend for TLS.
Reviewed-by: Jacob Hoffman-Andrews
Fixes#6955
Cloes #6956