gst-arch.m4 mixes CPUs with ABIs

Submitted by Sebastian Dröge @slomo

Link to original bug (#794605)

Description

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=893813

That is, x32 can't run x86-64 assembly but we detect it has x86-64 nonetheless. This causes the yadif plugin in gst-plugins-bad to fail compiling on x32 currently.

Not sure how meson handles this