- autotools: add support for custom prefix.
Usage: `--enable-versioned-symbols=MYPREFIX_`
Catching up with cmake.
- add default versioned prefix for Rustls builds.
- delete `HIDDEN` entry from version script `lib/libcurl.vers.in`.
It referred to symbol names that never existed in libcurl.
- cmake: use `lib/libcurl.vers.in` as a template instead of generating
it from scratch. Adapt `./configure` accordingly, and add comments
to keep hard-wired soname in sync with `lib/Makefile.soname`.
- autotools: delete Schannel and Secure Transport version prefixes.
Windows and macOS don't support the versioned symbols option.
Follow-up to 7b14449790#14378Closes#14818
- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING
checksrc is updated to allow non-year using copyright statements
Closes#10205