Add NetBSD support in test/tsan/thread_name*.cc

Summary:
A snipped from the documentation of thread_setname_np(3):

NAME
     pthread_getname_np - get and set descriptive name of a thread

LIBRARY
     POSIX Threads Library (libpthread, -lpthread)

SYNOPSIS
     #include <pthread.h>

     int
     pthread_getname_np(pthread_t thread, char *name, size_t len);

     int
     pthread_setname_np(pthread_t thread, const char *name, void *arg);

Sponsored by <The NetBSD Foundation>

Reviewers: joerg, dvyukov, eugenis, vitalybuka, kcc

Reviewed By: dvyukov

Subscribers: kubamracek, llvm-commits, #sanitizers

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D37306

llvm-svn: 312159