compile dyncall with -fPIC on DragonFly BSD
This fixes a build problem on DragonFly BSD.
It's the same fix as in commit 5ed99d26b3c3ac2d65bc622afdbd987a547046f5 for FreeBSD and 008f60c31bbd82ca090486468e8ffc8cd51bfb11 for NetBSD.
Merge pull request #184 from usev6/master

compile dyncall with -fPIC on DragonFly BSD