It was disabled because dlsym tests failed when PIC is on (#7640).
However, later it turned out that the issue is not related to PIC, and
LuaJIT was turned off for such tests by commit 67e79b15 ("test: turn
LuaJIT off in tests with dlsym"). Now it's safe to turn on PIC for FreeBSD.

Follow-up #7536

NO_DOC=build
NO_TEST=build

(cherry picked from commit 05eba830)