Do not blindly add libdl to extra libraries
Do not blindly add libdl to extra libraries

On some systems dlopen() is available without libdl (illumos, solaris).
Sometimes libdl.so cannot be loaded by runtime linker, see
https://ghc.haskell.org/trac/ghc/ticket/8713

Closes #8

rimmington/unix,rimmington/unix,rimmington/unix,rimmington/unix