Made ldl code a part of extern_ssba library, otherwise gcc fails to
find ldl symbols because order of libraries seems to be critical
for gcc linker.

A bit stupid, but that's how linker works..

Both CMake and SCons shall work fine on linux now.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54686 954f8c5b-7b00-dc11-b283-0030488c597c