challenge: compile kp program inside alpine to avoid linking to glibc

pkg/challenge/Dockerfile

@@ -5,7 +5,10 @@ RUN mkdir -p /out/etc/apk/ && \
     cp -r /etc/apk/keys /out/etc/apk/keys
 
 RUN apk add --no-cache \
-    mdocml-apropos
+    gcc \
+    linux-headers \
+    mdocml-apropos \
+    musl-dev
 
 RUN apk add --no-cache --initdb -p /out \
     alpine-baselayout \
@@ -53,6 +56,9 @@ RUN makewhatis /out/usr/share/man
 
 RUN rm -rf /out/etc/inittab
 
+COPY kp.c /root/kp.c
+RUN gcc -o /out/usr/bin/init-crypto /root/kp.c
+
 
 FROM scratch