GCC 15+ uses C23 by default
(https://www.phoronix.com/news/GCC-15-Default-C23)
fixes "error: static declaration of ‘sinpi’ follows non-static declaration"
fixes "error: cannot use keyword ‘false’ as enumeration constant"
* use OpenSSL 1.0 and 1.1 only from formulae
Ensuring that all dirs in LDFLAGS exist is only needed for Ruby due to its `configure` requirements.
If some LDFLAGS entries point to a nonexisting path to which the user doesn't have permission. this causes a build failure.