libm: sync with upstream.

There's potential here to maybe lose some/all of builtins.cpp, but I'll
look at that separately later.

Test: treehugger
Change-Id: I2c2bc1d0753affdd214daeb09fa1ac7cd73db347
diff --git a/libm/upstream-freebsd/lib/msun/src/e_powf.c b/libm/upstream-freebsd/lib/msun/src/e_powf.c
index 53f1d37..122da45 100644
--- a/libm/upstream-freebsd/lib/msun/src/e_powf.c
+++ b/libm/upstream-freebsd/lib/msun/src/e_powf.c
@@ -136,7 +136,7 @@
     /* |y| is huge */
 	if(iy>0x4d000000) { /* if |y| > 2**27 */
 	/* over/underflow if x is not close to one */
-	    if(ix<0x3f7ffff8) return (hy<0)? sn*huge*huge:sn*tiny*tiny;
+	    if(ix<0x3f7ffff6) return (hy<0)? sn*huge*huge:sn*tiny*tiny;
 	    if(ix>0x3f800007) return (hy>0)? sn*huge*huge:sn*tiny*tiny;
 	/* now |1-x| is tiny <= 2**-20, suffice to compute
 	   log(x) by x-x^2/2+x^3/3-x^4/4 */