[3.12] main/curl: security upgrade to 7.77.0
Contains fixes for the following vulnerabilities in 7.76.1:
- CVE-2021-22897
- CVE-2021-22898
- CVE-2021-22901
Also explicitly use OpenSSL as the TLS library, which is necessary following the merge of https://github.com/curl/curl/pull/6897.