mkalpine: install missing apps to build iso

I'm not sure if we really want this

mkalpine

@@ -1,5 +1,21 @@
 #!/bin/sh
 
+# check if what we need is here
+needed="cramfs syslinux cdrkit"
+for i in $needed; do
+	if ! apk info -e $i; then
+		missing="$missing $i"
+	fi
+done
+
+# try install the missing parts
+if [ -n "$missing" ]; then
+	if ! sudo apk add $missing; then
+		echo "Need $missing to build alpine" >&2
+		exit 1
+	fi
+fi
+
 # first look for alpine.mk in current dir. Fallback to /usr/share/abuild
 mk=./alpine.mk
 if ! [ -f $mk ]; then
@@ -7,3 +23,9 @@ if ! [ -f $mk ]; then
 fi
 
 make -f "$mk" APK_BIN= $@
+rc=$?
+
+# uninstall the stuff we installed
+[ -n "$missing" ] && sudo apk del $missing
+
+exit $?