Yes, the dynamic linker (/lib/ld-linux.so.2), which is one relatively short program as opposed to thousands of big ones. :)

The point is, there's simply no usecase to require or even allow the program to do IFUNC substitution freely on its own. A programming framework should not opt the developer in to capabilities they don't want or need. Much of C-likes' complexity arises from unnecessary, mandated capabilities.