HAVE_OPENSSL_EC doesn't get checked and set when building with a local version of OpenSSL, and the default is no EC support. As a consequence, scripts like ssl_cert.nse will display certs with elliptic curve keys as type "other" rather than as type "ec". This is becuase lua structures won't get populated in nse_ssl_cert.cc

and hence won't be available in nse lua scripts.
The root cause appears to be that the check at is not reached because it is inside the if at
which requires that $specialssldir is zero length, but it would be non-zero length if "--with-openssl" is specified, for example as "--with-openssl=/usr/local".
This particularly applies if the desire is to build nmap with static libraries and hence not wanting to put the local libraries and includes into the system default serach paths.
A hacky workaround is to explicitly add
#define HAVE_OPENSSL_EC 1
to nmap_config.h after running ./configure
Reproduction: Environment: Oracle Linux 7.9. Downloaded and built openssl 1.1.1m from openssl source tarball and "make install" to /usr/local. Downloaded nmap 7.92 source tarball,
$ ./configure --with-openssl=/usr/local --with-localdirs
$ grep HAVE_OPENSSL_EC nmap_config.h
/* #undef HAVE_OPENSSL_EC */'
$ grep EVP_PKEY_get1_EC_KEY /usr/local/lib64/libcrypto.so
000000000017be90 T EVP_PKEY_get1_EC_KEY