Remove support for IA64
There are many
#ifdef __ia64 in Ruby code base. At one point it must have been supported.
But as an architecture, it's EOL (Jan 30th 2019). Last CPU was released in 2017.
I can't even buy 2nd hand CPU for testing.
So, I propose we remove support for IA64.
The main motivation for me personally is I want to simplify and improve fiber implementation. But it's impossible for me to test IA64 architecture.