vsnprintf is called twice; one call must use args, and one must use
args2 (which is how it was supposed to be from the beginning). Each call
"consumes" its va_list parameter, so they each need to use a separate
copy. Fixes potential corruption and/or crashing when calling vsnprintf.
- Requires MbedTLS on Linux
- Enabled by default on macOS and Flatpak
- Enabled on linux via ENABLE_WHATSNEW_LINUX
- Enables compilation of blake2 on Linux/macOS
- Makes header name check also work with lowercase header
- Changes WahtsNew to be only enabled when browser panels are available