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/k_expl.h b/libm/upstream-freebsd/lib/msun/ld128/k_expl.h
index e843d43..4c041e8 100644
--- a/libm/upstream-freebsd/lib/msun/ld128/k_expl.h
+++ b/libm/upstream-freebsd/lib/msun/ld128/k_expl.h
@@ -1,6 +1,8 @@
 /* from: FreeBSD: head/lib/msun/ld128/s_expl.c 251345 2013-06-03 20:09:22Z kargl */
 
 /*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
  * Copyright (c) 2009-2013 Steven G. Kargl
  * All rights reserved.
  *
@@ -29,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD: head/lib/msun/ld128/k_expl.h 275819 2014-12-16 09:21:56Z ed $");
+__FBSDID("$FreeBSD: head/lib/msun/ld128/k_expl.h 326219 2017-11-26 02:00:33Z pfg $");
 
 /*
  * ld128 version of k_expl.h.  See ../ld80/s_expl.c for most comments.