Sync upstream FreeBSD libm.

Test: treehugger
Change-Id: I583a3e93821d512c975db34fc1610ffd22445d58
diff --git a/libm/upstream-freebsd/lib/msun/src/e_log2.c b/libm/upstream-freebsd/lib/msun/src/e_log2.c
index 4766cdb..10b1c00 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_log2.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_log2.c
@@ -39,7 +39,7 @@
 static volatile double vzero = 0.0;
 
 double
-__ieee754_log2(double x)
+log2(double x)
 {
 	double f,hfsq,hi,lo,r,val_hi,val_lo,w,y;
 	int32_t i,k,hx;