Makefile: Add implicit SELinux labels when using podman (#1598)

Podman is a Docker replacement, which is developed by RedHat and available
on related Linux distributions (e.g. RHEL or Fedora).  Podman differs from
Docker in several security-related aspects.  One of them is, that Podman
requires poper SELinux labels on volume content mounted into a container.
This difference to Docker results in the following error when building
the specification:

  Emulate Docker CLI using podman. Create /etc/containers/nodocker to quiet msg.
  /var/lib/gems/3.0.0/gems/asciidoctor-2.0.23/lib/asciidoctor/cli/options.rb:238:in `stat': Permission denied @ rb_file_s_stat - src/riscv-privileged.adoc (Errno::EACCES)
	from /var/lib/gems/3.0.0/gems/asciidoctor-2.0.23/lib/asciidoctor/cli/options.rb:238:in `block in parse!'
	from /var/lib/gems/3.0.0/gems/asciidoctor-2.0.23/lib/asciidoctor/cli/options.rb:236:in `each'
	from /var/lib/gems/3.0.0/gems/asciidoctor-2.0.23/lib/asciidoctor/cli/options.rb:236:in `parse!'
	from /var/lib/gems/3.0.0/gems/asciidoctor-pdf-2.3.18/bin/asciidoctor-pdf:40:in `<top (required)>'
	from /usr/local/bin/asciidoctor-pdf:25:in `load'
	from /usr/local/bin/asciidoctor-pdf:25:in `<main>'
  make[2]: *** [Makefile:92: build/riscv-privileged.pdf] Error 1

To address this, podman-run(1) recommends using the ':z' suffix to the
volume mount.  This patch does so, if the docker command has been
identified (reliably) to be emulated by Podman.

Tested on Fedora 40.

Signed-off-by: Christoph Müllner <[email protected]>

Makefile

@@ -24,8 +24,16 @@ DOCS := riscv-privileged riscv-unprivileged
 DATE ?= $(shell date +%Y-%m-%d)
 DOCKER_IMG := riscvintl/riscv-docs-base-container-image:latest
 ifneq ($(SKIP_DOCKER),true)
+	DOCKER_IS_PODMAN = \
+		$(shell ! docker -v 2>&1 | grep podman >/dev/null ; echo $$?)
+	ifeq "$(DOCKER_IS_PODMAN)" "1"
+		DOCKER_VOL_SUFFIX = :z
+	endif
+
 	DOCKER_CMD = \
-		docker run --rm -v ${PWD}/[email protected]:/build -w /build \
+		docker run --rm \
+			-v ${PWD}/[email protected]:/build${DOCKER_VOL_SUFFIX} \
+			-w /build \
 			${DOCKER_IMG} \
 			/bin/sh -c
 	DOCKER_QUOTE := "