I see that the first of those mentions it's for SunOS 5.11 whereas your machine says it's 5.10 ... is it possible the functions were new in 5.11?
I am not 100% sure. By the error, what i understand is that for some reason PostgreSQL version 9.5.x is expecting the SunOS version to be more recent than 5.10.
We would need to compile PostgreSQL-9.5.3 to upgrade our customer's production environments. We did not have problems compiling earlier versions of PostgreSQL.