math: Expm1 returns -1 with large negative argument.

Fixes #11442

Change-Id: I2053fe752c6a122924d28565f1338f73e00ed417
Reviewed-on: https://go-review.googlesource.com/11791
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/src/math/all_test.go b/src/math/all_test.go
index 84061be..6286584 100644
--- a/src/math/all_test.go
+++ b/src/math/all_test.go
@@ -946,16 +946,20 @@
 
 var vfexpm1SC = []float64{
 	Inf(-1),
+	-710,
 	Copysign(0, -1),
 	0,
+	710,
 	Inf(1),
 	NaN(),
 }
 var expm1SC = []float64{
 	-1,
+	-1,
 	Copysign(0, -1),
 	0,
 	Inf(1),
+	Inf(1),
 	NaN(),
 }