[Buildroot] [PATCH 1/2] package/Makefile.in should grab HOST_DIR headers using -isystem instead of -I.

[David Raeman <draeman@bbn.com>]

Yann, All,

On Fri, Jul 29, 2016 at 5:16 PM, Yann E. MORIN wrote:
> U-Boot or Qemu? I thought you needed that for your custom Qemu

The problem was revealed when I added a br2-external package for 
custom Qemu, but I traced the root issue to be with u-boot and how it
is impacted by the include directory added by HOST_CPPFLAGS.

The custom Qemu required me to install libfdt into the host area -
nothing wrong with doing that.  But having libfdt installed in
HOST_DIR causes u-boot to fail, because u-boot was finding libfdt.h 
in HOST_DIR/usr/include prior to searching its own directory for its
local modified copy of that same filename.

> And thus we should revert that patch. Will you send a patch to do the revert,
> please?

Yes I will.  I believe the patch to revert should also back out patch 
2/2 that installed libfdt to HOST_DIR as a part of host-dtc.  As 
mentioned above, if you keep that change and only revert the change to
HOST_CPPFLAGS, then u-boot to fail unless something else is done.  Do
you agree I should revert both changes with this new patch, to ensure
there is no leftover breakage?

> So, I think the best solution would be for U-Boot^WQemu to rename their
> header.

Given the various considerations, I agree this is the lowest-risk
solution.  Keeping in mind that any other package with a local header
file in conflict with a HOST_DIR header file can experience this same
problem.  The root issue is that usage of CPPFLAGS causes packages
to search HOST_DIR/usr/include before they search their local source
directories.

I may be a bit of time before I can submit a new patch to rename the
header file within u-boot.

Cheers,
David