__tls_get_addr@@GLIBC_2.3 undefined link error unless ld.so is passed as a link arg

[kkysen]

When compartmentalizing dav1d (run ./rewrite.py from immunant/dav1d/ia2), there was a link error saying __tls_get_addr@@GLIBC_2.3 was undefined. We were able to fix this by passing ld.so (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2) as a link arg, but I'm not sure why this is needed, and it wasn't needed before (this error used to not happen, and then all of a sudden it started happening, so I'm not sure what changed). Perhaps it has to do with the TLS "Local Exec" model error as well (#457)?