Update to FreeBSD libm r336665.

This reverts commit 253a8306316cedfd6fd3e3a169fbffe4cac04035 and moves
us forward to a revision that contains fixes for the problem with the
previous attempt.

This also makes sincos(3)/sincosf(3)/sincosl(3) available to `_BSD_SOURCE`
as well as `_GNU_SOURCE`.

The new FreeBSD libm code requires the FreeBSD `__CONCAT` macro, and all
our existing callers are FreeBSD too, so update that.

There's also an assumption that <complex.h> drags in <math.h> which isn't
true for us, so work around that with `-include` in the makefile. This
then causes clang to recognize a bug -- returning from a void function --
in our fake (LP32) sincosl(3), so fix that too.

Bug: http://b/111710419
Change-Id: I84703ad844f8afde6ec6b11604ab3c096ccb62c3
Test: ran tests
diff --git a/libm/upstream-freebsd/lib/msun/ld128/s_expl.c b/libm/upstream-freebsd/lib/msun/ld128/s_expl.c
index a6a9676..53bc04a 100644
--- a/libm/upstream-freebsd/lib/msun/ld128/s_expl.c
+++ b/libm/upstream-freebsd/lib/msun/ld128/s_expl.c
@@ -1,4 +1,6 @@
 /*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
  * Copyright (c) 2009-2013 Steven G. Kargl
  * All rights reserved.
  *
@@ -27,7 +29,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
+__FBSDID("$FreeBSD: head/lib/msun/ld128/s_expl.c 326219 2017-11-26 02:00:33Z pfg $");
 
 /*
  * ld128 version of s_expl.c.  See ../ld80/s_expl.c for most comments.