zig: use via apk

That way we won't need to bump zig versions with new releases.

Dockerfile

@@ -1,22 +1,13 @@
-FROM alpine
+FROM alpine:edge
 
-# zig is installed from the upstream tarball, because:
-# - as of writing, alpine has zig only in testing (which is cumbersome to use)
-# - apk get zig pulls in libllvm, which is huge.
-#
-# Upstream tarball is statically linked, making it small and convenient to use.
-RUN apk add make \
- && wget https://ziglang.org/download/0.12.0/zig-linux-$(uname -m)-0.12.0.tar.xz \
- && tar -xJf zig-linux-*.tar.xz \
- && rm zig-linux-*.xz \
- && mv zig-linux-* zig
+RUN apk add make zig
 
 WORKDIR inotify-info
 
 COPY . .
 
-RUN CC="/zig/zig cc -target $(uname -m)-linux-musl" \
-    CXX="/zig/zig c++ -target $(uname -m)-linux-musl" \
+RUN CC="zig cc -target $(uname -m)-linux-musl" \
+    CXX="zig c++ -target $(uname -m)-linux-musl" \
     make
 
 FROM scratch