Enable the exception option

This is to cause an immediate build error if the zlib download fails.

Author: ledsun

lib/ruby_wasm/build_system/product/zlib.rb

@@ -35,7 +35,8 @@ def build
       FileUtils.rm_rf product_build_dir
 
       system "curl -L https://zlib.net/zlib-#{ZLIB_VERSION}.tar.gz | tar xz",
-             chdir: File.dirname(product_build_dir)
+             chdir: File.dirname(product_build_dir),
+             exception: true
 
       system "#{tools_args.join(" ")} ./configure --static",
              chdir: product_build_dir