common : clarify HTTPS build options in error message (ggml-org#19103)

* common : clarify HTTPS build options in error message

This commit updates the https error message to provide clearer
instructions for users who encounter the "HTTPS is not supported" error.

The motivation for this is that it might not be clear to users that only
one of these options are needed to enable HTTPS support.
The LLAMA_OPENSSL option is also added to the message to cover all
possible build configurations.

* clarify that OpenSSL is the default for HTTPS support

Author: danbev

common/http.h

@@ -60,10 +60,10 @@ static std::pair<httplib::Client, common_http_url> common_http_client(const std:
 #ifndef CPPHTTPLIB_OPENSSL_SUPPORT
     if (parts.scheme == "https") {
         throw std::runtime_error(
-            "HTTPS is not supported. Please rebuild with:\n"
+            "HTTPS is not supported. Please rebuild with one of:\n"
             "  -DLLAMA_BUILD_BORINGSSL=ON\n"
             "  -DLLAMA_BUILD_LIBRESSL=ON\n"
-            "or ensure dev files of an OpenSSL-compatible library are available when building."
+            "  -DLLAMA_OPENSSL=ON (default, requires OpenSSL dev files installed)"
         );
     }
 #endif