test: add build constraints to Unix-only files (#11712)

test/fuse_dlm, test/fuse_p2p/peer_chunk_sharing_test.go and
unmaintained/check_disk_size use syscall.Flock, syscall.Stat_t and
syscall.Statfs, which do not exist on Windows. Without constraints,
gopls and go vet on a Windows host report them as undefined.

fuse_p2p/framework_test.go already carries `linux || darwin`; the FUSE
test files now match it. check_disk_size uses the same constraint as
weed/stats/disk_supported.go.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/fuse_dlm/dlm_concurrent_write_test.go

@@ -1,3 +1,5 @@
+//go:build linux || darwin
+
 package fuse_dlm
 
 import (

test/fuse_dlm/framework_test.go

@@ -1,3 +1,5 @@
+//go:build linux || darwin
+
 package fuse_dlm
 
 import (

test/fuse_dlm/posix_lock_ring_test.go

@@ -1,3 +1,5 @@
+//go:build linux || darwin
+
 package fuse_dlm
 
 import (

test/fuse_p2p/peer_chunk_sharing_test.go

@@ -1,3 +1,5 @@
+//go:build linux || darwin
+
 package fuse_p2p
 
 import (

unmaintained/check_disk_size/check_disk_size.go

@@ -1,3 +1,5 @@
+//go:build !windows && !openbsd && !netbsd && !plan9 && !solaris
+
 package main
 
 import (