fsck_msdosfs: add a test for reconnecting on volumes larger than 4 GiBHEADmain

Build a 4.5 GiB FAT32 image whose LOST.DIR cluster sits exactly 4 GiB above
the single cluster of a PAYLOAD.BIN, so that truncating the offset of the
former to 32 bits yields the offset of the latter, then inject a lost cluster
chain and let fsck_msdosfs(8) reconnect it.

The test asserts both halves of the bug fixed in the previous commit: that
PAYLOAD.BIN's cluster is unchanged, and that a second pass no longer reports
the chain as lost, which it only stops doing once the directory entry reaches
the real LOST.DIR.

newfs_msdos(8) -C only calls ftruncate(2) and nothing outside the reserved
area, the FATs and a handful of clusters is ever written, so the image stays
sparse and costs about 2 MiB on disk.

The geometry is read back out of the BPB rather than assumed, so
newfs_msdos(8) stays free to lay the file system out differently; the test
fails with a clear message if the volume ever becomes too small to hold a
cluster a full 4 GiB beyond the data area.

MFC after:	1 week

0 files changed, 0 insertions, 0 deletions