I've never seen an organization that didn't do a full rebuild of every build product contained in each release anyway. Usually it's just faster and less error-prone to do a full rebuild than to recompile the minimal set of source files and relink.
On Linux there's a large gray area for things like libexpat.so.1 that may or may not be linked dynamically. But libc is LGPL, so I expect it too would be linked dynamically.