Add the prof_sys_thread_name feature in the prof_recent unit test.

This tests the combination of the prof_recent and thread_name features.
Verified that it catches the issue being fixed in this PR.

Also explicitly set thread name in test/unit/prof_recent.  This fixes the name
testing when no default thread name is set (e.g. FreeBSD).

test/src/thd.c

@@ -32,3 +32,21 @@ thd_join(thd_t thd, void **ret) {
 	pthread_join(thd, ret);
 }
 #endif
+
+void
+thd_setname(const char *name) {
+#ifdef JEMALLOC_HAVE_PTHREAD_SETNAME_NP
+	pthread_setname_np(pthread_self(), name);
+#elif defined(JEMALLOC_HAVE_PTHREAD_SET_NAME_NP)
+	pthread_set_name_np(pthread_self(), name);
+#endif
+}
+
+bool
+thd_has_setname(void) {
+#if defined(JEMALLOC_HAVE_PTHREAD_SETNAME_NP) || defined(JEMALLOC_HAVE_PTHREAD_SET_NAME_NP)
+	return true;
+#else
+	return false;
+#endif
+}