Add configure and CMake options to define CURL_DISABLE_NEGOTIATE_NTLM,
which gates the NTLM blocking logic in the SSPI and GSS-API SPNEGO
code paths behind a compile-time flag.
Add a 'SPNEGO-no-NTLM' feature string to curl --version output and
gate the SPNEGO NTLM blocking tests on the negotiate-ntlm-disabled
feature.
Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>