debian: make cross-compile work

This allows e.g. "sbuild --host=arm64" to build packages for other
architectures on, say, fat amd64 servers.  As a side effect, the Debian
build uses a separate builddir, which helps noting issues on that front.

Signed-off-by: David Lamparter <equinox@diac24.net>
(cherry-picked from commit d1312e009b)

debian/control

@@ -25,10 +25,10 @@ Build-Depends: bison,
                libyang2-dev,
                lsb-base,
                pkg-config,
-               python3,
-               python3-dev,
-               python3-pytest <!nocheck>,
-               python3-sphinx,
+               python3:native,
+               python3-dev:native,
+               python3-pytest:native <!nocheck>,
+               python3-sphinx:native,
                texinfo (>= 4.7),
                lua5.3 <pkg.frr.lua>,
                liblua5.3-dev <pkg.frr.lua>

debian/frr-doc.info

@@ -1 +1 @@
-doc/user/_build/texinfo/frr.info
+build/doc/user/_build/texinfo/frr.info

debian/frr.manpages

@@ -1,16 +1,16 @@
-doc/manpages/_build/man/frr-bgpd.8
-doc/manpages/_build/man/frr-eigrpd.8
-doc/manpages/_build/man/frr-fabricd.8
-doc/manpages/_build/man/frr-isisd.8
-doc/manpages/_build/man/frr-ldpd.8
-doc/manpages/_build/man/frr-nhrpd.8
-doc/manpages/_build/man/frr-ospf6d.8
-doc/manpages/_build/man/frr-ospfd.8
-doc/manpages/_build/man/frr-pimd.8
-doc/manpages/_build/man/frr-ripd.8
-doc/manpages/_build/man/frr-ripngd.8
-doc/manpages/_build/man/frr-watchfrr.8
-doc/manpages/_build/man/frr-zebra.8
-doc/manpages/_build/man/frr.1
-doc/manpages/_build/man/mtracebis.8
-doc/manpages/_build/man/vtysh.1
+build/doc/manpages/_build/man/frr-bgpd.8
+build/doc/manpages/_build/man/frr-eigrpd.8
+build/doc/manpages/_build/man/frr-fabricd.8
+build/doc/manpages/_build/man/frr-isisd.8
+build/doc/manpages/_build/man/frr-ldpd.8
+build/doc/manpages/_build/man/frr-nhrpd.8
+build/doc/manpages/_build/man/frr-ospf6d.8
+build/doc/manpages/_build/man/frr-ospfd.8
+build/doc/manpages/_build/man/frr-pimd.8
+build/doc/manpages/_build/man/frr-ripd.8
+build/doc/manpages/_build/man/frr-ripngd.8
+build/doc/manpages/_build/man/frr-watchfrr.8
+build/doc/manpages/_build/man/frr-zebra.8
+build/doc/manpages/_build/man/frr.1
+build/doc/manpages/_build/man/mtracebis.8
+build/doc/manpages/_build/man/vtysh.1

debian/rules

@@ -36,7 +36,7 @@ endif
 export PYTHON=python3
 
 %:
-	dh $@
+	dh $@ -Bbuild
 
 override_dh_auto_configure:
 	$(shell dpkg-buildflags --export=sh); \
@@ -78,9 +78,9 @@ override_dh_auto_install:
 	sed -e '1c #!/usr/bin/python3' -i debian/tmp/usr/lib/frr/generate_support_bundle.py
 
 # let dh_systemd_* and dh_installinit do their thing automatically
-	cp tools/frr.service debian/frr.service
-	cp tools/frr@.service debian/frr@.service
-	cp tools/frrinit.sh debian/frr.init
+	cp build/tools/frr.service debian/frr.service
+	cp build/tools/frr@.service debian/frr@.service
+	cp build/tools/frrinit.sh debian/frr.init
 	-rm -f debian/tmp/usr/lib/frr/frr
 
 # install config files
@@ -114,6 +114,11 @@ override_dh_makeshlibs:
 override_dh_missing:
 	dh_missing --fail-missing
 
+ifneq ($(filter nocheck,$(DEB_BUILD_PROFILES) $(DEB_BUILD_OPTIONS)),)
+override_dh_auto_test:
+	true
+endif
+
 override_dh_auto_clean:
 # we generally do NOT want a full distclean since that wipes both
 # debian/changelog and config.version