Make it easy to use different versions of Fedora for static checks

Fedora 33 is the last Fedora version that works on RHEL 7 (see
https://bugzilla.redhat.com/show_bug.cgi?id=1962080 for details),
but if people have newer container runtimes, they can use Fedora
34, 35 or whatever future brings. Let's just make that easy.

Makefile.am

@@ -167,6 +167,9 @@ destroy-vms:
 static-check:
 	tests/static-check/run.sh
 
+static-check-f%:
+	STATIC_CHECKS_FEDORA_VERSION=$* tests/static-check/run.sh
+
 #
 # Get everything removed down to where rebuilding requires:
 # "make; make install"

tests/static-check/run.sh

@@ -3,21 +3,31 @@
 set -e
 trap "echo FAILURE" ERR
 
-set -x
-BASE_IMG="fedora:33"
+if [ -z "$STATIC_CHECKS_FEDORA_VERSION" ]; then
+  # Fedora 33 is the default because it works with old container runtimes
+  # (see https://bugzilla.redhat.com/show_bug.cgi?id=1962080 and linked bugs for
+  # details)
+  echo "No Fedora version for static checks specified, using the default (Fedora 33)"
+  BASE_IMG="fedora:33"
+  STATIC_CHECKS_FEDORA_VERSION="33"
+else
+  BASE_IMG="fedora:$STATIC_CHECKS_FEDORA_VERSION"
+fi
 
 function create_image() {
   local c=$(buildah from -q $BASE_IMG)
   buildah run $c -- dnf -q -y install "@C Development Tools and Libraries" clang cppcheck which >/dev/null 2>&1
   buildah run $c -- dnf -q -y install pcre-devel openssl-devel libxml2-devel pam-devel lmdb-devel libacl-devel libyaml-devel curl-devel libvirt-devel >/dev/null 2>&1
   buildah run $c -- dnf clean all >/dev/null 2>&1
-  buildah commit $c cfengine-static-checker >/dev/null 2>&1
+  buildah commit $c cfengine-static-checker-f$STATIC_CHECKS_FEDORA_VERSION >/dev/null 2>&1
   echo $c
 }
 
+set -x
+
 # TODO: check how old the image is and recreate if it's too old
-if buildah inspect cfengine-static-checker >/dev/null 2>&1; then
-  c=$(buildah from cfengine-static-checker)
+if buildah inspect cfengine-static-checker-f$STATIC_CHECKS_FEDORA_VERSION >/dev/null 2>&1; then
+  c=$(buildah from cfengine-static-checker-f$STATIC_CHECKS_FEDORA_VERSION)
 else
   c=$(create_image)
 fi