math: update Gamma special cases
Match new C99 values for special cases.

Fixes #2977.

R=rsc, golang-dev
CC=golang-dev
https://golang.org/cl/5972058
diff --git a/src/pkg/math/all_test.go b/src/pkg/math/all_test.go
index ed66a42..8cbead1 100644
--- a/src/pkg/math/all_test.go
+++ b/src/pkg/math/all_test.go
@@ -1128,11 +1128,11 @@
 	NaN(),
 }
 var gammaSC = []float64{
+	NaN(),
+	NaN(),
 	Inf(-1),
 	Inf(1),
 	Inf(1),
-	Inf(1),
-	Inf(1),
 	NaN(),
 }