I can confirm that building a GSS-API library (and its support libraries) with the default platform alignment works, setting SNC_LIB to the path to libgssapi_krb5.dylib.
I applied the top commit from https://github.com/kaduk/krb5/commits/sap and built MIT krb5 locally, as I'm more familiar with that build system than the native OS X Heimdal. Note that MIT krb5 does not currently understand the default API credentials cache used by the base system Kerberos installation, so the hand-build kinit should be used as well as the GSS-API library.
This is a way to get the SAP client running on a developer's system, but it does not seem like the optimal strategy for deployment on user workstations. I am still investigating building a shim around the system-provided GSS-API library as a SNC Adapter.