support ldflags rewrites for initialized globals

cl/_testgo/rewrite/main.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"fmt"
+	"runtime"
+
+	dep "github.com/goplus/llgo/cl/_testgo/rewrite/dep"
+)
+
+var VarName = "main-default"
+var VarPlain string
+
+func printLine(label, value string) {
+	fmt.Printf("%s: %s\n", label, value)
+}
+
+func main() {
+	printLine("main.VarName", VarName)
+	printLine("main.VarPlain", VarPlain)
+	dep.PrintVar()
+	printLine("runtime.GOROOT()", runtime.GOROOT())
+	printLine("runtime.Version()", runtime.Version())
+}