pthread_atfork undefined link error in permissive mode

[kkysen]

When compartmentalizing dav1d and building with permissive mode (run ./rewrite.py --permissive-mode from immunant/dav1d/ia2), there's a link error saying pthread_atfork is undefined. pthread_atfork is called at

IA2-Phase2/runtime/libia2/include/permissive_mode.h

Line 461 in 94f890b

pthread_atfork(NULL, NULL, IA2_IGNORE(install_permissive_mode_handler));

, and so commenting out this call allows things to compile and link, but doesn't fix the issue, and will probably break if fork is ever called. pthread_atfork is defined in libc.so, and providing libc.so as an explicit argument did not work like it did for __tls_get_addr@@GLIBC_2.3 and ld.so. Furthermore, this error used to not happen, and then all of a sudden it started happening, so I'm not sure what changed.