Detect pthread_getname_np explicitly.

At least one libc (musl) defines pthread_setname_np without defining
pthread_getname_np. Detect the presence of each individually, rather than
inferring both must be defined if set is.

src/prof_sys.c

@@ -292,8 +292,11 @@ void prof_unwind_init() {
 
 static int
 prof_sys_thread_name_read_impl(char *buf, size_t limit) {
-#ifdef JEMALLOC_HAVE_PTHREAD_SETNAME_NP
+#if defined(JEMALLOC_HAVE_PTHREAD_GETNAME_NP)
 	return pthread_getname_np(pthread_self(), buf, limit);
+#elif defined(JEMALLOC_HAVE_PTHREAD_GET_NAME_NP)
+	pthread_get_name_np(pthread_self(), buf, limit);
+	return 0;
 #else
 	return ENOSYS;
 #endif