kernel & addons: Build with the non-legacy GCC even on x86_gcc2h.

Only one code change: for some reason, GCC chokes on the cr3 functions
as macros (throwing errors about invalid registers.) The BSDs have them
as inline functions instead, so they are converted to that here.

Tested and working. There seems to be about a 10% decrease in CPU time
on some compilation benchmarks that I briefly tried.

Change-Id: I31666297394d7619f83fca6ff5f933ddd6f07420
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4515
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

Revert "Jamfiles: Repace TARGET_PACKAGING_ARCH with TARGET_KERNEL_ARCH in a few places."

This reverts commit 66833143276573a3aa68600d3b38e56bc6e2aa7b.

Revert "Jamfiles: Repace TARGET_PACKAGING_ARCH with TARGET_KERNEL_ARCH in a few places."

Previous revert inadvertently staged a different version. That's what I get for
rebasing 3 things at one time...

This reverts commit 66833143276573a3aa68600d3b38e56bc6e2aa7b.

Revert "Jamfiles: Repace TARGET_PACKAGING_ARCH with TARGET_KERNEL_ARCH in a few places."

This reverts commit 66833143276573a3aa68600d3b38e56bc6e2aa7b.

Apparently, on closer inspection, this is not actually correct:
TARGET_KERNEL_ARCH is "x86" even on gcc2, and not an index into
the TARGET_CC_* etc. variable sets. That is pretty confusing and should
probably be fixed.

Jamfiles: Repace TARGET_PACKAGING_ARCH with TARGET_KERNEL_ARCH in a few places.

This is more technically correct.

Move DeviceOpener class to a separate file.

It is used by several of the filesystems, so it seems a good idea to
move it to the shared/ directory.

UFS2, BFS, XFS, EXT2 and EXFAT are adjusted.

Change-Id: I493e37a1e7d3ae24251469f82befd985a3c1dbdd
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2489
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

bfs: add stub for ResizeVisitor.

This allows to have all the tools (resizefs, fs_shell, etc) merged, and
split out the remaining BFS resize changes in a way that makes some
sense. We can easily merge all the basic infrastructure (ioctls, etc)
without any of the actual resizing code (I'll leave that to
professionals).

BFS: Only compile with -O1 under GCC2.

GCC7+ does not have whatever compiler bugs plague GCC2, so we can
use -O2 there as usual.

BFS: Add support for building big-endian BFS

I tried to use the feature stuff to relocate objects but didn't managed
to get it to work, having another subdir seems to be the simplest
solution.

I managed to mount a clone of my BeBox' drive, but it KDLed shortly when mouting
read-write.

Change-Id: Ia4f126673e553e4f3e524a40218e6c623527b96d
Reviewed-on: https://review.haiku-os.org/c/645
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>