We also remove conditionalization for garbage collector inclusion in autotools.
When we propose an alternative gc, then we may decide to put them back, or to
add necessary ifdef statements directly in files.
Moreover untangle c-stack from the gc code and assign the stack base with a
rough guess only when it is not initialized yet (GC will always fill it).
Finally remove a kludge from ecl_adopt_cpu and disable colleciton until the cpu
is fully initialized.
6116a83fbb