From the error message I deduce, that you are building the (unreleased) tip version of NaviServer from bitbucket, and you are building against an unknown (unsupported) version of OpenSSL installed. If i see correctly, ECDSA_SIG was introduced to OpenSSL in 2016 in version 0.9.8. What version of OpenSSL are you using? Are you using some alternative version of OpenSSL?
The support of ECDSA (Elliptic Curve Digital Signature Algorithm) in NaviServer is currently extended, since the demand for crypto support in web servers is on the rise. Also, the OpenSSL crypto API is changing. Certainly, NaviServer should still build (with reduced functionality) on system like yours
all the best
-gn
