Add a filelock for in-place case

Multiple bpmodify process on the same Android.bp can run in parallel in
the case of aidl-freeze-api.

So, add a file lock for in-place editing case(-w)

Bug: 229413853
Test: run bpmodify in parallel and check result
Change-Id: I5368b0304b59f34fff60025120b38cc5f615ac40

bpmodify/bpmodify.go

@@ -15,6 +15,7 @@ import (
 	"os/exec"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"unicode"
 
 	"github.com/google/blueprint/parser"
@@ -68,6 +69,11 @@ func processFile(filename string, in io.Reader, out io.Writer) error {
 			return err
 		}
 		defer f.Close()
+
+		if *write {
+			syscall.Flock(int(f.Fd()), syscall.LOCK_EX)
+		}
+
 		in = f
 	}