Add zig version helper script

build.zig.version

@@ -0,0 +1 @@
+0.12.0-dev.2817+7461309b7

zig

@@ -0,0 +1,37 @@
+#!/bin/bash
+set -e
+
+ARCH=$(uname -m)
+
+BASEDIR="$(cd "$(dirname "$0")" && pwd)"
+ZIGDIR=$BASEDIR/.cache/zig
+VERSION=$(< build.zig.version)
+ZIGVER="zig-linux-$ARCH-$VERSION"
+ZIG=$ZIGDIR/$ZIGVER/zig
+
+if [ "$1" == "update" ] ; then
+    curl -L --silent https://ziglang.org/download/index.json | jq -r '.master | .version' > build.zig.version
+    NEWVERSION=$(< build.zig.version)
+
+    if [ "$VERSION" != "$NEWVERSION" ] ; then
+        echo zig version updated from $VERSION to $NEWVERSION
+        exit 0
+    fi
+    echo zig version $VERSION is up-to-date
+    exit 0
+fi
+    
+get_zig() {
+    (
+        mkdir -p "$ZIGDIR"
+        cd "$ZIGDIR"
+        TARBALL="https://ziglang.org/builds/$ZIGVER.tar.xz"
+
+        if [ ! -d "$ZIGVER" ] ; then
+            curl "$TARBALL" | tar -xJ
+        fi
+    )
+}
+get_zig
+
+exec $ZIG "$@"