tsan: yet another attempt to fix pthread_cond interceptors
Make behavior introduced in r202820 conditional (under legacy_pthread_cond flag).
The new issue that we've hit with the satellite pthread_cond_t struct is
that pthread_condattr_getpshared does not work (satellite data is not shared between processes).
The idea is that most processes do not use pthread 2.2.5.
The rare ones that use (2.2.5 is dated by 2002) must specify legacy_pthread_cond=1
on their own risk.