Support compiling without fuse2 headers

[SuperSandro2000]

Right now compiling only with fuse3 headers fails like:

rclone> # github.com/winfsp/cgofuse/fuse
rclone> vendor/github.com/winfsp/cgofuse/fuse/host_cgo.go:119:10: fatal error: fuse.h: No such file or directory
rclone>   119 | #include <fuse.h>
rclone>       |          ^~~~~~~~
rclone> compilation terminated.

The layout for fuse3 is slightly different. It would be cool to support this as fuse2 is really unmaintained.

├──  include
│   └──  fuse3
│       ├──  cuse_lowlevel.h
│       ├──  fuse.h
│       ├──  fuse_common.h
│       ├──  fuse_log.h
│       ├──  fuse_lowlevel.h
│       ├──  fuse_opt.h
│       └──  libfuse_config.h