Commit b7033a8

build: fetch the zig tarball for the host arch

The Dockerfile hardcoded the x86_64 tarball, so on an arm64 host the
image ran under emulation and `zig build` died before compiling anything:

    error: rosetta error: bss_size overflow

That made `zmx run build`, `test`, `fmt`, and `integration` from pico.sh
unusable on Apple silicon.

`uname -m` already reports the names zig uses (x86_64, aarch64), so
substituting it needs no mapping table. Unknown arches now fail with
their own name rather than a 404 from ziglang.org.

Also drop `-v` from tar, which printed a line per extracted file, and
remove the tarball after extracting it.

 1@@ -3,11 +3,19 @@ FROM debian:12
 2 RUN apt-get update && apt-get install -y curl git bats coreutils && rm -rf /var/lib/apt/lists/*
 3 
 4 ARG ZIG_VERSION=0.16.0
 5-RUN curl -L -o /tmp/zig.tar.xz https://ziglang.org/download/${ZIG_VERSION}/zig-x86_64-linux-${ZIG_VERSION}.tar.xz && \
 6+# `uname -m` already reports the names zig uses in its tarballs (x86_64,
 7+# aarch64), so it needs no mapping.
 8+RUN ARCH="$(uname -m)" && \
 9+	case "$ARCH" in \
10+	  x86_64|aarch64) ;; \
11+	  *) echo "unsupported arch: $ARCH" >&2; exit 1 ;; \
12+	esac && \
13+	curl -L -o /tmp/zig.tar.xz https://ziglang.org/download/${ZIG_VERSION}/zig-${ARCH}-linux-${ZIG_VERSION}.tar.xz && \
14 	cd /tmp && \
15-	tar -xvf zig.tar.xz && \
16-  mv zig-x86_64-linux-${ZIG_VERSION} /usr/local/zig && \
17-  ln -s /usr/local/zig/zig /usr/local/bin/zig
18+	tar -xf zig.tar.xz && \
19+	mv zig-${ARCH}-linux-${ZIG_VERSION} /usr/local/zig && \
20+	ln -s /usr/local/zig/zig /usr/local/bin/zig && \
21+	rm -f /tmp/zig.tar.xz
22 
23 ENV PATH=/usr/local/zig:$PATH
24