BUILD: fix build on Solaris 11

BUILD: fix build on Solaris 11

htonll()/ntohll() already exist on Solaris 11 with a different declaration,
causing a build error as reported by Jonathan Fisher. They used to exist on
OSX with a #define which allowed us to detect them. It was a bad idea to give
these functions a name subject to conflicts like this. Simply rename them
my_htonll()/my_ntohll() to definitely get rid of the conflict.

This patch must be backported to 1.6.