configure: Put cross compile flags in EXTRA_CFLAGS

The cross compile CFLAGS are needed to properly build pixman (and any other
submodules). Only the EXTRA_CFLAGS set is passed to submodules not QEMU_CFLAGS,
so put the cross compile flags in EXTRA_CFLAGS instead.

Signed-off-by: Peter Crosthwaite peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
dtc: add submodule

Add dtc submodule as a fallback for old distros.
Picking version 1.3.0. as this is the most recently tagged stable version.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>
configure/Make: Build libfdt from submodule DTC

Configure to use the DTC submodule to build libfdt when no system libfdt
is found. Prompt to install the DTC submodule if --enable-fdt is set but
no DTC can be found.

DTC has no out-of-tree build capability, so the configure will symlink
the Makefile and scripts directory in the out of tree build directory
and pass in all the needed DTC arguments to make out of tree build happen.
Ideally we fix the DTC make to support out of tree, but did it this way to
avoid commits to DTC.

Signed-off-by: David Holsgrove <david.holsgrove@xilinx.com>
Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@gmail.com>