dashboard: add SSA check builder

Now that SSA checks are off by default, let's run a builder with the
checks on just to make sure they keep passing.

Change-Id: I7edd2a2865681a135ccf755be7a14f8645c0a8aa
Reviewed-on: https://go-review.googlesource.com/20882
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

dashboard/builders.go

@@ -340,6 +340,13 @@ func init() {
 		//BuildletType: "linux-amd64",
 		env: []string{"GOROOT_BOOTSTRAP=/go1.4", "GO_GCFLAGS=-N -l"},
 	})
+	addBuilder(BuildConfig{
+		Name:    "linux-amd64-ssacheck",
+		Notes:   "SSA internal checks enabled",
+		VMImage: "linux-buildlet-std",
+		//BuildletType: "linux-amd64",
+		env: []string{"GOROOT_BOOTSTRAP=/go1.4", "GO_GCFLAGS=-d=ssa/check/on"},
+	})
 	addBuilder(BuildConfig{
 		Name:           "linux-amd64-race",
 		VMImage:        "linux-buildlet-std",