tsan: disable getpwent interceptors

There interceptors do not seem to be strictly necessary for tsan.
But we see cases where the interceptors consume 70% of execution time.
Memory blocks passed to fgetgrent_r are "written to" by tsan several times.
First, there is some recursion (getgrnam_r calls fgetgrent_r), and each
function "writes to" the buffer. Then, the same memory is "written to"
twice, first as buf and then as pwbufp (both of them refer to the same addresses).