fallible_collections crate fails to build on i686 arch

Hello everyone

While trying to fix the build of the `rust-fallible_collections` package 
I found out [1] that the crate does not work properly with 32 bit systems.
I am not quite sure if my findings are 100% accurate but lets say they 
are. What would be the best option here? Adding "ExcludeArch" to the 
spec file?

Thank you for you answers in advance!

Hussein

[1] https://github.com/vcombey/fallible_collections/issues/35