Also check writable tty and raise if unavailable

Author: headius

extconf.rb

@@ -10,14 +10,18 @@
     WARNING:
     WARNING: See https://github.com/rbenv/ruby-build/pull/2517 for more details.
   MSG
-  if File.exist?("/dev/tty")
+
+  # extconf.rb runs in a captured subprocess, so the only way to output is via /dev/tty
+  if File.exist?("/dev/tty") && File.writable?("/dev/tty")
     error << <<~MSG
       WARNING:
       WARNING: The native jruby executable has not been installed.
     MSG
     File.write("/dev/tty", error)
   else
+    # /dev/tty is not available, so write to stderr and raise
     $stderr.write(error)
+    raise
   end
   File.write("Makefile", dummy_makefile($srcdir).join(""))
   return