Configure: Remove extra warning and sanitizer options from CXXFLAGS

We add the extra warning and sanitizer options to check our code,
which is entirely in C.  We support C++ compilers uniquely for the
sake of certain external test suites, and those projects can probably
sanitize their own code themselves.

[extended tests]

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/9013)