fix Linux build: use golang.org/x/sys/unix for Fadvise

Replace syscall.Fadvise with unix.Fadvise from golang.org/x/sys/unix
which is the correct portable way to access fadvise on Linux

internal/bsdaily/copy_linux.go

@@ -4,13 +4,13 @@ package bsdaily
 
 import (
 	"os"
-	"syscall"
+	"golang.org/x/sys/unix"
 )
 
 func applyFileAdvice(file *os.File, size int64) {
 	fd := int(file.Fd())
 	// POSIX_FADV_SEQUENTIAL = 2
-	_ = syscall.Fadvise(fd, 0, size, 2)
+	_ = unix.Fadvise(fd, 0, size, 2)
 	// POSIX_FADV_WILLNEED = 3 - prefetch file into cache
-	_ = syscall.Fadvise(fd, 0, size, 3)
+	_ = unix.Fadvise(fd, 0, size, 3)
 }