UBUNTU: [Packaging] do not attempt to generate BTF header on armhf

BugLink: https://bugs.launchpad.net/bugs/2050083

armhf does not have working BTF for now, so create an empty header file
like Debian does for now, to be dropped once that issue is fixed.

Follow-up for aefbe1e1a9a1d3ed84bceac7e9739a92e1345f58

Signed-off-by: Luca Boccassi <bluca@debian.org>

[ add do_tools_bpftool_stub to avoid hardcoding the arch in rules ]
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>
(cherry-picked from commit 0c32444afa9bd036e66cbc8c05dbd8df8388bc6f oracular:linux)
Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>

debian.master/rules.d/armhf.mk

@@ -13,6 +13,7 @@ do_tools_perf	= true
 do_tools_perf_jvmti = true
 do_tools_perf_python = true
 do_tools_bpftool = true
+do_tools_bpftool_stub = true
 do_tools_rtla = true
 
 do_dtbs		= true

debian/rules.d/2-binary-arch.mk

@@ -683,7 +683,11 @@ endif
 ifeq ($(do_tools_bpftool),true)
 	mv $(builddirpa)/tools/bpf/bpftool/vmlinux $(builddirpa)/vmlinux
 	$(kmake) CROSS_COMPILE=$(CROSS_COMPILE) -C $(builddirpa)/tools/bpf/bpftool
+ifneq ($(do_tools_bpftool_stub),true)
 	$(builddirpa)/tools/bpf/bpftool/bpftool btf dump file $(builddirpa)/vmlinux format c > $(builddirpa)/vmlinux.h
+else
+	echo '#error "Kernel does not support CONFIG_DEBUG_INFO_BTF"' > $(builddirpa)/vmlinux.h
+endif
 	rm -f $(builddirpa)/vmlinux
 endif
 ifeq ($(do_tools_x86),true)