libm: sync with upstream FreeBSD.

Bug: http://b/143311272
Test: ran tests
Change-Id: I0fbf94fb5cd13e64a55957d0f951757746d0367a
diff --git a/libm/upstream-freebsd/lib/msun/src/s_expm1f.c b/libm/upstream-freebsd/lib/msun/src/s_expm1f.c
index c0a3934..4d9ab36 100644
--- a/libm/upstream-freebsd/lib/msun/src/s_expm1f.c
+++ b/libm/upstream-freebsd/lib/msun/src/s_expm1f.c
@@ -14,7 +14,7 @@
  */
 
 #include <sys/cdefs.h>
-__FBSDID("$FreeBSD$");
+__FBSDID("$FreeBSD: head/lib/msun/src/s_expm1f.c 352710 2019-09-25 18:50:57Z dim $");
 
 #include <float.h>
 
@@ -94,7 +94,7 @@
 	e  = hxs*((r1-t)/((float)6.0 - x*t));
 	if(k==0) return x - (x*e-hxs);		/* c is 0 */
 	else {
-	    SET_FLOAT_WORD(twopk,0x3f800000+(k<<23));	/* 2^k */
+	    SET_FLOAT_WORD(twopk,((u_int32_t)(0x7f+k))<<23);	/* 2^k */
 	    e  = (x*(e-c)-c);
 	    e -= hxs;
 	    if(k== -1) return (float)0.5*(x-e)-(float)0.5;