Fix moving files

using os.Rename to move files fails when copying files between different
partitions. On Debian 10 it failes with an "invalid cross-device link"
error. The solution is to copy the source file to the destination and
then remove the source.

go-fuzz-build/main.go

@@ -121,10 +121,7 @@ func main() {
 
 	if *flagLibFuzzer {
 		archive := c.buildInstrumentedBinary(&blocks, nil)
-		err := os.Rename(archive, *flagOut)
-		if err != nil {
-			c.failf("failed to rename file: %v", err)
-		}
+		c.moveFile(archive, *flagOut)
 		return
 	}
 
@@ -663,10 +660,7 @@ func (c *Context) instrumentPackages(blocks *[]CoverBlock, sonar *[]CoverBlock)
 			if runtime.GOOS == "windows" {
 				os.Remove(outpath)
 			}
-			err := os.Rename(tmp, outpath)
-			if err != nil {
-				c.failf("failed to rename file: %v", err)
-			}
+			c.moveFile(tmp, outpath)
 		}
 	}
 
@@ -710,6 +704,14 @@ func (c *Context) copyFile(src, dst string) {
 	}
 }
 
+func (c *Context) moveFile(src, dst string) {
+	c.copyFile(src, dst)
+	err := os.Remove(src)
+	if err != nil {
+		c.failf("moveFile: removing %q failed: %v", src, err)
+	}
+}
+
 func (c *Context) failf(str string, args ...interface{}) {
 	c.cleanup()
 	fmt.Fprintf(os.Stderr, str+"\n", args...)