but not /usr/include/ruby-1.9.1/i486-linux/. You may need to pass /usr/include/ruby-1.9.1/i486-linux/ as an extra include directory to the build process.
Er, this is a variable (arch-dependent) string. e.g. on my system it is
/usr/include/ruby-1.9.1/x86_64-linux
Clearly the Ruby build system has some way of returning the include path required to build programs that embed the Ruby interpreter. Looking at some other program that embeds Ruby should make it clear what that is. (I'd look, but it's mercilessly hot here and I haven't slept for days, so I'm feeling decidedly lazy...)
Yes, I agree. Earlier today I sent a report to the list sharing what I had discovered about the build failure. Looks like that message got lost while the servers were cut off from the world.
I'll repost that message.
Darrell