Raise an error if the host is using an older kernel than the target.
Since qemu-user passes emulated system calls to the host kernel,
this prevents usage of qemu-user in situations where those system
calls will fail.
This is based on an original patch from Frank Hunleth
<fhunleth@troodon-software.com>, but completely rewritten in a
different way:
* Instead of using shell based testing, we use pure make tests, which
allows to detect the problem not when host-qemu starts to build,
but at the very beginning of the entire Buildroot build.
* Instead of looking at $(STAGING_DIR)/usr/include/linux/version.h
(which requires having a dependency on the 'toolchain' package,
which is a bit unusual for a host package), we use the
BR2_TOOLCHAIN_HEADERS_AT_LEAST Config.in option which tells us the
version of the kernel headers used in the toolchain.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Frank Hunleth <fhunleth@troodon-software.com>
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