Add a HAVE define for pthread_setname_np().

Due to conflicts with recent WebKit, we need to call it
HAVE_ANDROID_PTHREAD_SETNAME_NP.

https://review.source.android.com/#change,15227 has the original
change, which was reverted after the conflict was found.

Change-Id: I7111960a16505558338756dba91eb50cadb582ff