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: Fix 32 bit gcc2 compile.

You can't initialize struct fields in the declaration in gcc2, but you
can set them up in a constructor. So made one for struct diri,
and initialize nested sub-structures too.

Change-Id: Ic8b824bc157cca4cdb8c4e41afdca596776c0d55
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4995
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

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>