Just a few notes:
1. This change is asking for trouble. "gc" is already used as the
library name of Boehm GC, which we are linking to, so these internal
GC components should be called "libinkgc" instead to avoid possible
naming conflicts.
2. The convention so far was that "lib*" directories in the source
tree are for in-tree forks/copies of third party libraries (except
"libnrtype").