support ldflags rewrites for initialized globals

cl/_testgo/rewrite/dep/dep.go

@@ -0,0 +1,11 @@
+package dep
+
+import "fmt"
+
+var VarName = "dep-default"
+var VarPlain string
+
+func PrintVar() {
+	fmt.Printf("dep.VarName: %s\n", VarName)
+	fmt.Printf("dep.VarPlain: %s\n", VarPlain)
+}