d/rules.real: Export CROSS_COMPILE_COMPAT, CROSS32_COMPILE variables
On arm64 the config symbol COMPAT_VDSO has a dependency on
$(CROSS_COMPILE_COMPAT) being non-empty. This requires that
CROSS_COMPILE_COMPAT is an environment variable.
Since 6.4~rc7-1~exp1 we set CROSS_COMPILE_COMPAT in .kernelvariables.
Unlike ARCH and CROSS_COMPILE, this is not exported by the upstream
Makefile, so the dependencies of COMPAT_VDSO were not satisified.
In earlier versions debian/rules.gen passed CROSS_COMPILE_COMPAT on
the make command line for debian/rules.real, which automatically made
it an environment variable too (TIL) despite the lack of an explicit
export.
Change the generation of .kernelvariables to export
CROSS_COMPILE_COMPAT. While we're here, do the same for
CROSS32_COMPILE so that if parisc or powerpc start using it in config
that will also work.
This re-enables the compat vDSO on arm64.
Fixes: 71d03aa1 ("linux-image: Define CROSS_COMPILE and ...")