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/src/e_fmod.c b/libm/upstream-freebsd/lib/msun/src/e_fmod.c
index bad066a..fbb2d93 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_fmod.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_fmod.c
@@ -12,7 +12,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD: head/lib/msun/src/e_fmod.c 305380 2016-09-04 12:01:32Z bde $");
+__FBSDID("$FreeBSD: head/lib/msun/src/e_fmod.c 336663 2018-07-24 10:10:16Z bde $");
 
 /* 
  * __ieee754_fmod(x,y)
@@ -42,7 +42,7 @@
     /* purge off exception values */
 	if((hy|ly)==0||(hx>=0x7ff00000)||	/* y=0,or x not finite */
 	  ((hy|((ly|-ly)>>31))>0x7ff00000))	/* or y is NaN */
-	    return (x*y)/(x*y);
+	    return nan_mix_op(x, y, *)/nan_mix_op(x, y, *);
 	if(hx<=hy) {
 	    if((hx<hy)||(lx<ly)) return x;	/* |x|<|y| return x */
 	    if(lx==ly)