kbuild: rpm-pkg: disable kernel-devel package when cross-compiling

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

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

$ make ARCH=arm64 CROSS_COMPILE=aarch64-suse-linux- binrpm-pkg
[ snip ]
Rebuilding host programs with aarch64-suse-linux-gcc...
HOSTCC /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/kallsyms
HOSTCC /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sorttable
HOSTCC /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/asn1_compiler
HOSTCC /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sign-file
/home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sign-file.c:25:10: fatal error: openssl/opensslv.h: No such file or directory
25 | #include <openssl/opensslv.h>
| ^~~~~~~~~~~~~~~~~~~~
compilation terminated.

I believe this issue is less common on Fedora because the disto's cross-
compilier cannot link user-space programs. Hence, CONFIG_CC_CAN_LINK is
unset.

On Fedora 40, the package information explains this limitation clearly:

$ dnf info gcc-aarch64-linux-gnu
[ snip ]
Description : Cross-build GNU C compiler.
:
: Only building kernels is currently supported. Support for cross-building
: user space programs is not currently provided as that would massively multiply
: the number of packages.

Anyway, cross-compiling RPM packages is somewhat challenging.

This commit disables the kernel-devel package when cross-compiling
because I did not come up with a better solution.

Fixes: f1d87664b82a ("kbuild: cross-compile linux-headers package when possible")
Signed-off-by: Masahiro Yamada <[e-mail]>
Reviewed-by: Nathan Chancellor <[e-mail]>

scripts/Makefile.package

···
 
 PHONY += rpm-pkg srcrpm-pkg binrpm-pkg
 
+ifneq ($(CC),$(HOSTCC))
+rpm-no-devel = --without=devel
+endif
+
 rpm-pkg:    private build-type := a
 srcrpm-pkg: private build-type := s
 binrpm-pkg: private build-type := b
···
 	--define='_topdir $(abspath rpmbuild)' \
 	$(if $(filter a b, $(build-type)), \
 		--target $(UTS_MACHINE)-linux --build-in-place --noprep --define='_smp_mflags %{nil}' \
-		$$(rpm -q rpm >/dev/null 2>&1 || echo --nodeps)) \
+		$$(rpm -q rpm >/dev/null 2>&1 || echo --nodeps) \
+		$(rpm-no-devel)) \
 	$(RPMOPTS))
 
 # deb-pkg srcdeb-pkg bindeb-pkg