deb-pkg: Fix cross-building linux-headers package

builddeb generates a control file that says the linux-headers package
can only be built for the build system primary architecture.  This
breaks cross-building configurations.  We should use $debarch for this
instead.

Since $debarch is not yet set when generating the control file, set
Architecture: any and use control file variables to fill in the
description.

Fixes: cd8d60a20a45 ('kbuild: create linux-headers package in deb-pkg')
Reported-and-tested-by: "Niew, Sh." <shniew@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/package/builddeb

@@ -62,7 +62,7 @@ create_package() {
 	fi
 
 	# Create the package
-	dpkg-gencontrol -isp $forcearch -p$pname -P"$pdir"
+	dpkg-gencontrol -isp $forcearch -Vkernel:debarch="${debarch:-$(dpkg --print-architecture)}" -p$pname -P"$pdir"
 	dpkg --build "$pdir" ..
 }
 
@@ -298,15 +298,14 @@ mkdir -p "$destdir"
 (cd $objtree; cp $KCONFIG_CONFIG $destdir/.config) # copy .config manually to be where it's expected to be
 ln -sf "/usr/src/linux-headers-$version" "$kernel_headers_dir/lib/modules/$version/build"
 rm -f "$objtree/debian/hdrsrcfiles" "$objtree/debian/hdrobjfiles"
-arch=$(dpkg --print-architecture)
 
 cat <<EOF >> debian/control
 
 Package: $kernel_headers_packagename
 Provides: linux-headers, linux-headers-2.6
-Architecture: $arch
-Description: Linux kernel headers for $KERNELRELEASE on $arch
- This package provides kernel header files for $KERNELRELEASE on $arch
+Architecture: any
+Description: Linux kernel headers for $KERNELRELEASE on \${kernel:debarch}
+ This package provides kernel header files for $KERNELRELEASE on \${kernel:debarch}
  .
  This is useful for people who need to build external modules
 EOF