packaging: Enable cross-building agent

Requires setting ARCH and CC.

- Add CC linker option for building agent.
- Set host for building libseccomp.

Fixes: #3681
Signed-off-by: Jakob Naucke <jakob.naucke@ibm.com>

ci/install_libseccomp.sh

@@ -19,7 +19,7 @@ source "${tests_repo_dir}/.ci/lib.sh"
 # fail. So let's ensure they are unset here.
 unset PREFIX DESTDIR
 
-arch=$(uname -m)
+arch=${ARCH:-$(uname -m)}
 workdir="$(mktemp -d --tmpdir build-libseccomp.XXXXX)"
 
 # Variables for libseccomp
@@ -70,7 +70,8 @@ build_and_install_gperf() {
     curl -sLO "${gperf_tarball_url}"
     tar -xf "${gperf_tarball}"
     pushd "gperf-${gperf_version}"
-    ./configure --prefix="${gperf_install_dir}"
+    # Unset $CC for configure, we will always use native for gperf
+    CC= ./configure --prefix="${gperf_install_dir}"
     make
     make install
     export PATH=$PATH:"${gperf_install_dir}"/bin
@@ -84,7 +85,7 @@ build_and_install_libseccomp() {
     curl -sLO "${libseccomp_tarball_url}"
     tar -xf "${libseccomp_tarball}"
     pushd "libseccomp-${libseccomp_version}"
-    ./configure --prefix="${libseccomp_install_dir}" CFLAGS="${cflags}" --enable-static
+    ./configure --prefix="${libseccomp_install_dir}" CFLAGS="${cflags}" --enable-static --host="${arch}"
     make
     make install
     popd

utils.mk

@@ -113,7 +113,8 @@ endef
 BUILD_TYPE = release
 
 ##VAR ARCH=arch target to build (format: uname -m)
-ARCH = $(shell uname -m)
+HOST_ARCH = $(shell uname -m)
+ARCH ?= $(HOST_ARCH)
 ##VAR LIBC=musl|gnu
 LIBC ?= musl
 ifneq ($(LIBC),musl)
@@ -142,6 +143,14 @@ ifeq ($(ARCH), aarch64)
     $(warning "WARNING: aarch64-musl needs extra symbols from libgcc")
 endif
 
+ifneq ($(HOST_ARCH),$(ARCH))
+    ifeq ($(CC),)
+         CC = gcc
+         $(warning "WARNING: A foreign ARCH was passed, but no CC alternative. Using gcc.")
+    endif
+    override EXTRA_RUSTFLAGS += -C linker=$(CC)
+endif
+
 TRIPLE = $(ARCH)-unknown-linux-$(LIBC)
 
 CWD := $(shell dirname $(realpath $(firstword $(MAKEFILE_LIST))))