[lldb] [test] Fix TestGdbRemoteThreadName code on FreeBSD

[mgorny]

Summary

Fix TestGdbRemoteThreadName to call ::pthread_setname_np instead
of ::pthread_set_name_np on FreeBSD. While technically both names
are correct, the former is preferable because of compatibility
with Linux. Furthermore, the latter requires #include <pthread_np.h>
that was missing causing the test to fail to compile.

[mgorny]

Note that D90863 is also required to fix the test.

lldb/test/API/tools/lldb-server/thread-name/main.cpp

 #include <pthread.h>
 #include <signal.h>
 
 void set_thread_name(const char *name) {
 #if defined(__APPLE__)
   ::pthread_setname_np(name);
-#elif defined(__FreeBSD__)
-  ::pthread_set_name_np(::pthread_self(), name);
-#elif defined(__linux__)
+#elif defined(__FreeBSD__) || defined(__linux__)
   ::pthread_setname_np(::pthread_self(), name);
 #elif defined(__NetBSD__)
   ::pthread_setname_np(::pthread_self(), "%s", const_cast<char *>(name));
 #endif
 }
 
 int main() {
   set_thread_name("hello world");
   raise(SIGINT);
   set_thread_name("goodbye world");
   raise(SIGINT);
   return 0;
 }