[fix] Embed custom jemalloc into libaml
Force libtool to static link the PIC version of our jemalloc import into libaml, making libaml standalone. This requires us to test some additional libraries in our own configure (pthread, and dlopen). This also solves the long-standing issue of `make check` only working after `make install`, while removing our custom jemalloc from the installed libraries. Fixes #26.