We are in the process of updating glslang, which requires
set(IOS_MIN_TARGET "13.0")
This is a problem since we are targeting iOS 11 in general.
glslang is a filamat depedency, and we're building filamat for
iOS for the iOS version of the backend test.
So one solution is to set set(IOS_MIN_TARGET "13.0") for the
backend test. And we might revisit this solution later.
But for now, we simply disable backend tests (and filamat tests)
for iOS.
defba23030