Enable more CLIF tests on AArch64

The tests for the SIMD floating-point maximum and minimum operations
require particular care because the handling of the NaN values is
non-deterministic and may vary between platforms. There is no way to
match several NaN values in a test, so the solution is to extract the
non-deterministic test cases into a separate file that is subsequently
replicated for every backend under test, with adjustments made to the
expected results.

Copyright (c) 2021, Arm Limited.

cranelift/filetests/src/test_simple_preopt.rs

@@ -23,6 +23,10 @@ impl SubTest for TestSimplePreopt {
         "simple_preopt"
     }
 
+    fn needs_isa(&self) -> bool {
+        true
+    }
+
     fn is_mutating(&self) -> bool {
         true
     }