speed: fix build for Go 1.4 and lower

Old Go versions miss cipher.NewGCMWithNonceSize, which causes:

  internal/speed/speed.go:95: undefined: cipher.NewGCMWithNonceSize

3 files changed, 15 insertions, 0 deletions

diff --git a/internal/speed/speed.go b/internal/speed/speed.go
index f9bf93c..bc829d4 100644
--- a/internal/speed/speed.go
+++ b/internal/speed/speed.go
@@ -1,3 +1,5 @@
+// +build go1.5
+
 // Package speed implements the "-speed" command-line option,
 // similar to "openssl speed".
 // It benchmarks the crypto algorithms and libraries used by
diff --git a/internal/speed/speed_go1.4.go b/internal/speed/speed_go1.4.go
new file mode 100644
index 0000000..9c0125c
--- /dev/null
+++ b/internal/speed/speed_go1.4.go
@@ -0,0 +1,11 @@
+// +build !go1.5
+
+package speed
+
+import (
+	"fmt"
+)
+
+func Run() {
+	fmt.Printf("Compile with Go 1.5 or higher to run the benchmarks\n")
+}
diff --git a/internal/speed/speed_test.go b/internal/speed/speed_test.go
index 1e9d859..d6bc187 100644
--- a/internal/speed/speed_test.go
+++ b/internal/speed/speed_test.go
@@ -1,3 +1,5 @@
+// +build go1.5
+
 package speed
 
 /*