kbuild: deb-pkg: add pkg.linux-upstream.nokernelheaders build profile

Since commit f1d87664b82a ("kbuild: cross-compile linux-headers package
when possible"), 'make bindeb-pkg' may attempt to cross-compile the
linux-headers package, but it fails under certain circumstances.

For example, when CONFIG_MODULE_SIG_FORMAT is enabled on Debian, the
following command fails:

$ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bindeb-pkg
[ snip ]
Rebuilding host programs with aarch64-linux-gnu-gcc...
HOSTCC debian/linux-headers-6.12.0-rc4/usr/src/linux-headers-6.12.0-rc4/scripts/kallsyms
HOSTCC debian/linux-headers-6.12.0-rc4/usr/src/linux-headers-6.12.0-rc4/scripts/sorttable
HOSTCC debian/linux-headers-6.12.0-rc4/usr/src/linux-headers-6.12.0-rc4/scripts/asn1_compiler
HOSTCC debian/linux-headers-6.12.0-rc4/usr/src/linux-headers-6.12.0-rc4/scripts/sign-file
In file included from /usr/include/openssl/opensslv.h:109,
from debian/linux-headers-6.12.0-rc4/usr/src/linux-headers-6.12.0-rc4/scripts/sign-file.c:25:
/usr/include/openssl/macros.h:14:10: fatal error: openssl/opensslconf.h: No such file or directory
14 | #include <openssl/opensslconf.h>
| ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

This commit adds a new profile, pkg.linux-upstream.nokernelheaders, to
guard the linux-headers package.

There are two options to fix the above issue.

Option 1: Set the pkg.linux-upstream.nokernelheaders build profile

$ DEB_BUILD_PROFILES=pkg.linux-upstream.nokernelheaders \
make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- bindeb-pkg

This skips the building of the linux-headers package.

Option 2: Install the necessary build dependencies

If you want to cross-compile the linux-headers package, you need to
install additional packages.

For example, on Debian, the packages necessary for cross-compiling it
to arm64 can be installed with the following commands:

# dpkg --add-architecture arm64
# apt update
# apt install gcc-aarch64-linux-gnu libssl-dev:arm64

Fixes: f1d87664b82a ("kbuild: cross-compile linux-headers package when possible")
Reported-by: Ron Economos <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Masahiro Yamada <[e-mail]>
Tested-by: Ron Economos <[e-mail]>
Reviewed-by: Nicolas Schier <[e-mail]>

scripts/package/builddeb

···
 	pdir=debian/$1
 	version=${1#linux-headers-}
 
-	"${srctree}/scripts/package/install-extmod-build" "${pdir}/usr/src/linux-headers-${version}"
+	CC="${DEB_HOST_GNU_TYPE}-gcc" "${srctree}/scripts/package/install-extmod-build" "${pdir}/usr/src/linux-headers-${version}"
 
 	mkdir -p $pdir/lib/modules/$version/
 	ln -s /usr/src/linux-headers-$version $pdir/lib/modules/$version/build

scripts/package/install-extmod-build

···
 	fi
 } | tar -c -f - -T - | tar -xf - -C "${destdir}"
 
-# When ${CC} and ${HOSTCC} differ, we are likely cross-compiling. Rebuild host
-# programs using ${CC}. This assumes CC=${CROSS_COMPILE}gcc, which is usually
-# the case for package building. It does not cross-compile when CC=clang.
+# When ${CC} and ${HOSTCC} differ, rebuild host programs using ${CC}.
 #
 # This caters to host programs that participate in Kbuild. objtool and
 # resolve_btfids are out of scope.
-if [ "${CC}" != "${HOSTCC}" ] && is_enabled CONFIG_CC_CAN_LINK; then
+if [ "${CC}" != "${HOSTCC}" ]; then
 	echo "Rebuilding host programs with ${CC}..."
 
 	cat <<-'EOF' >  "${destdir}/Kbuild"

scripts/package/mkdebian

···
 
 echo $debarch > debian/arch
 
+host_gnu=$(dpkg-architecture -a "${debarch}" -q DEB_HOST_GNU_TYPE | sed 's/_/-/g')
+
 # Generate a simple changelog template
 cat <<EOF > debian/changelog
 $sourcename ($packageversion) $distribution; urgency=low
···
 Maintainer: $maintainer
 Rules-Requires-Root: no
 Build-Depends: debhelper-compat (= 12)
-Build-Depends-Arch: bc, bison, cpio, flex, kmod, libelf-dev:native, libssl-dev:native, rsync
+Build-Depends-Arch: bc, bison, cpio, flex,
+ gcc-${host_gnu} <!pkg.${sourcename}.nokernelheaders>,
+ kmod, libelf-dev:native,
+ libssl-dev:native, libssl-dev <!pkg.${sourcename}.nokernelheaders>,
+ rsync
 Homepage: https://www.kernel.org/
 
 Package: $packagename-$version
···
 
 Package: linux-headers-$version
 Architecture: $debarch
+Build-Profiles: <!pkg.${sourcename}.nokernelheaders>
 Description: Linux kernel headers for $version on $debarch
  This package provides kernel header files for $version on $debarch
  .