dieHook: Add die utility function

Calling `die "Error message"` causes the current script to exit with
an error, printing a backtrace

pkgs/build-support/setup-hooks/die.sh

@@ -0,0 +1,21 @@
+# Exit with backtrace and error message
+#
+# Usage: die "Error message"
+die() {
+    # Let us be a little sloppy with errors, because otherwise the final
+    # invocation of `caller` below will cause the script to exit.
+    set +e
+
+    # Print our error message
+    printf "\nBuilder called die: %b\n" "$*"
+    printf "Backtrace:\n"
+
+    # Print a backtrace.
+    local frame=0
+    while caller $frame; do
+        ((frame++));
+    done
+    printf "\n"
+
+    exit 1
+}