make release: add cross-build

This implements cross-build for "make release", moving the build into a
container. This way we can support arm, arm64, ppc, and whatnot.

* script/seccomp.sh: separate out of script/release.sh, amend to support
  cross-compile and save needed environment variables to a file.

* Dockerfile: add installing libseccomp from source, as this is needed
  for release builds.

* script/release.sh: amend to support more architectures in addition to
  the native build. Additional arches can be added by specifying
  "-a <arch>" argument (can be specified multiple times), or
  "make RELEASE_ARGS="-a arm64" release" if called via make.
  All supported architectures can be enabled via "make releaseall".

* Makefile: move "release" target to "localrelease", add "release" and
  "releaseall" targets to build via the Dockerfile. This is done because
  most distros (including Fedora and openSUSE) lack cross-glibc, which is
  needed to cross-compile libseccomp.

* Makefile: remove 'cross' and 'localcross' targets, as this is now done
  by the release script.

* .github/workflows/validate.yum: amend the release CI job to cross-build
  for supported architectures, remove cross job.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Dockerfile

@@ -1,5 +1,6 @@
 ARG GO_VERSION=1.17
 ARG BATS_VERSION=v1.3.0
+ARG LIBSECCOMP_VERSION=2.5.1
 
 FROM golang:${GO_VERSION}-bullseye
 ARG DEBIAN_FRONTEND=noninteractive
@@ -21,15 +22,10 @@ RUN echo 'deb https://download.opensuse.org/repositories/devel:/tools:/criu/Debi
         curl \
         gawk \
         gcc \
+        gperf \
         iptables \
         jq \
         kmod \
-        libseccomp-dev \
-        libseccomp-dev:arm64 \
-        libseccomp-dev:armel \
-        libseccomp-dev:armhf \
-        libseccomp-dev:ppc64el \
-        libseccomp2 \
         pkg-config \
         python3-minimal \
         sudo \
@@ -52,4 +48,10 @@ RUN cd /tmp \
     && ./install.sh /usr/local \
     && rm -rf /tmp/bats-core
 
+# install libseccomp
+ARG LIBSECCOMP_VERSION
+COPY script/* /tmp/script/
+RUN mkdir -p /usr/local/src/libseccomp \
+    && /tmp/script/seccomp.sh "$LIBSECCOMP_VERSION" /usr/local/src/libseccomp /usr/local/src/libseccomp/.env-file arm64 armel armhf ppc64le
+
 WORKDIR /go/src/github.com/opencontainers/runc