Hi,
It seems since pkgsrc2020Q1 OpenSSL fails to compile on Solaris 10. In fact, pkgsrc2020Q1 switched from OpenSSL 1.0 to OpenSSL 1.1.
It seems it is a known issue by the OpenSSL team:
So as stated by the OpenSSL team, the quick fix would be to add the following line to your pkgsrc OpenSSL Makefile :
LDFLAGS+= -lrt
It's tested and working on my side.
There is certainly a better way to implement it but I'll leave it to you guys.