Compile LibreSSL alongside OpenSSL for curl in Linux distributions and vcpkg

[talregev]

Currently, many Linux distributions and vcpkg are unable to ship curl with LibreSSL due to compilation conflicts with OpenSSL. These conflicts arise from naming clashes in libraries and functions.
LibreSSL is an excellent candidate for providing HTTP/3 support in curl. If LibreSSL could be compiled alongside OpenSSL, this integration would already be possible.
It's worth noting that curl already releases Windows binaries with LibreSSL + HTTP/3 support (using ngtcp2 and nghttp3), as seen on their official website: https://curl.se/windows/

Proposal:

• Implement changes to allow LibreSSL to compile alongside OpenSSL
• Add LibreSSL support for curl in vcpkg
• Create an HTTP/3 feature for curl in vcpkg using LibreSSL

These modifications would greatly enhance the flexibility and capabilities of curl across various platforms and package managers.
Your thoughts and contributions on this matter are welcome.