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).

llvm-svn: 216904