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_fmodf.c b/libm/upstream-freebsd/lib/msun/src/e_fmodf.c
index 52ce373..3783a88 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_fmodf.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_fmodf.c
@@ -14,7 +14,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
+__FBSDID("$FreeBSD: head/lib/msun/src/e_fmodf.c 336663 2018-07-24 10:10:16Z bde $");
 
 /*
  * __ieee754_fmodf(x,y)
@@ -41,7 +41,7 @@
     /* purge off exception values */
 	if(hy==0||(hx>=0x7f800000)||		/* y=0,or x not finite */
 	   (hy>0x7f800000))			/* or y is NaN */
-	    return (x*y)/(x*y);
+	    return nan_mix_op(x, y, *)/nan_mix_op(x, y, *);
 	if(hx<hy) return x;			/* |x|<|y| return x */
 	if(hx==hy)
 	    return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/