buildmaster: add static apk utility

We need apk to sign packages.adb, this is unreleased version introduced
in commit ef8c1adb6118 ("apk: switch to index-trust branch"), thus not
available already anywhere yet. So until its available, lets build a
static version and use that meanwhile.

Fixes: a94d4e1 ("add APK signing logic")
Signed-off-by: Petr Štetiar <ynezz@true.cz>

docker/buildmaster/Dockerfile

@@ -1,3 +1,29 @@
+FROM alpinelinux/build-base:latest-x86_64 AS apk-builder
+
+RUN abuild-apk add -u \
+	gcc \
+	git \
+	linux-headers \
+	lua5.3-dev \
+	lua5.3-lzlib \
+	make \
+	musl-dev \
+	openssl-dev \
+	openssl-libs-static \
+	zlib-dev \
+	zlib-static \
+	zstd-dev \
+	zstd-static
+
+ARG APK_TOOLS_COMMIT=54caa31be633efc5f655700b77af290124f71689
+
+RUN git clone https://gitlab.alpinelinux.org/alpine/apk-tools.git /tmp/apk-tools
+WORKDIR /tmp/apk-tools
+RUN git fetch --depth=1 origin $APK_TOOLS_COMMIT
+RUN git reset --hard $APK_TOOLS_COMMIT
+RUN make -j$(nproc) static
+
+
 FROM        debian:11
 MAINTAINER  OpenWrt Maintainers
 
@@ -55,6 +81,7 @@ COPY docker/buildmaster/files/start.sh /start.sh
 COPY phase1 /phase1
 COPY phase2 /phase2
 COPY scripts /scripts
+COPY --from=apk-builder /tmp/apk-tools/src/apk.static /usr/bin/apk
 
 RUN \
     groupadd buildbot && \

tests/cram/master/02-apk.t

@@ -0,0 +1,4 @@
+Check that apk is available and usable in master container:
+
+  $ docker run local/master apk | grep usage
+  usage: apk [<OPTIONS>...] COMMAND [<ARGUMENTS>...]