Add --fail flag to curl download commands

By default, curls downloads the HTML error page and exits with code 0 when a server replies with a HTTP error code (e.g., 404), causing a SHA256 mismatch afterwards.

Adding the `--fail` flag makes curl exit with non-zero error code and print an error like "The requested URL returned error: 404", making it a bit easier to diagnose distfile download issues.

Also replaced `-L` with `--location` for the sake of script readability.

sysa/helpers.sh

@@ -208,7 +208,7 @@ interpret_source_line() {
     # Default to basename of url if not given
     fname="${fname:-$(basename "${url}")}"
     if ! [ -e "${fname}" ]; then
-        curl -L "${url}" --output "${fname}"
+        curl --fail --location "${url}" --output "${fname}"
     fi
     echo "${checksum}  ${fname}" > "${fname}.sum"
     sha256sum -c "${fname}.sum"