Print OS information on build failure

This is useful info for when someone is pasting build output to our
issue tracker seeking support.

bin/ruby-build

@@ -71,10 +71,21 @@ colorize() {
   fi
 }
 
+os_information() {
+  if type -p lsb_release >/dev/null; then
+    lsb_release -sir | xargs echo
+  elif type -p sw_vers >/dev/null; then
+    echo "OS X $(sw_vers -productVersion)"
+  else
+    local os="$(cat /etc/{centos,redhat,fedora,system}-release /etc/debian_version 2>/dev/null | head -1)"
+    echo "${os:-$(uname -sr)}"
+  fi
+}
+
 build_failed() {
   { echo
     colorize 1 "BUILD FAILED"
-    echo " ($(version))"
+    echo " ($(os_information) using $(version))"
     echo
 
     if ! rmdir "${BUILD_PATH}" 2>/dev/null; then