Revert "Update to FreeBSD libm r336523."

This reverts commit f86ee10278116d211cfb08679416444e0e714cb5.

Incorrect result for fmodf(3.0f, 0f) = 1.0f breaks ART tests.

Bug: 111710419
Test: art/test/testrunner/testrunner.py -b -t 436-rem-float --target
Change-Id: I7eae68fb92740db33415d16418447bcbbd98ecba
diff --git a/libm/upstream-freebsd/lib/msun/src/e_atan2f.c b/libm/upstream-freebsd/lib/msun/src/e_atan2f.c
index 0ce9bc0..fc77bff 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_atan2f.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_atan2f.c
@@ -14,7 +14,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD: head/lib/msun/src/e_atan2f.c 336362 2018-07-17 07:42:14Z bde $");
+__FBSDID("$FreeBSD$");
 
 #include "math.h"
 #include "math_private.h"
@@ -41,7 +41,7 @@
 	iy = hy&0x7fffffff;
 	if((ix>0x7f800000)||
 	   (iy>0x7f800000))	/* x or y is NaN */
-	    return nan_mix(x, y);
+	   return x+y;
 	if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
 	m = ((hy>>31)&1)|((hx>>30)&2);	/* 2*sign(x)+sign(y) */