file_systems/fat: Fix duplicateExpression

Pointed out by cppcheck

Change-Id: I21314d0724fd1b7ae74c575197aa3b50fb75db55
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7256
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

fat: record time of file modification

* Add a function that updates the last-modified time of a fat
vnode; call it when the driver writes, creates, deletes,
or moves a file.
* The function optionally copies the new time from the vnode to the
corresponding direntry (useful if the calling function is not
going to do that anyway).
* Add a function that updates the last-modified time of the parent
directory of a fat vnode and copies the new time to the corresponding
direntry; call it when the driver deletes a file (not needed
for creating or moving because the parent directory vnodes are
directly accessible).
* Fixes #11119.

Change-Id: Ic7c0bda55190f236e9fd31d5d140d753138f7997
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5798
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

FAT: enable -Werror

Change-Id: I4364d1325d4822d7094e985991c97639038522b8
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5436
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

FAT: Unlock before calling the file cache.

Otherwise if the file cache calls us again from a different thread,
as it sometimes does when doing concurrent I/O to multiple files,
we will deadlock.

Fixes #14104.

FAT: More miscellaneous cleanup.

* Remove __RO__ hack inherited from BeOS sample code.
* Remove and excise unneeded macros.
* Remove readlink, VFS will return EINVAL in its absence anyway.

FAT: Make more use of C++ features and utility classes.

This driver was fully C until relatively recently, when it was
switched to C++ so that it could be used with fs_shell. However,
it still is mostly using C paradigms; so this commit begins the
refactor away from that.

If I did this correctly, there should not be any functional change.

Change-Id: Id87d17b2e019ccdd1c7f07156cfe2a2124496675
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4725
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

file_system/fat: Rework driver for fs_shell support

* Introduce fat_shell for build system fat manipulation
* Will theoretically let us do away with mtools when we
have another internal tool for partition manipulation

Change-Id: I661be556e79009842f157a9402c8f85da85d6336
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3556
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>