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/filetests/legalizer/bxor_imm.clif

@@ -1,4 +1,5 @@
 test legalizer
+target aarch64
 target x86_64
 
 function %foo(i64, i64) -> i64 {

cranelift/filetests/filetests/legalizer/iconst-i64.clif

@@ -1,4 +1,5 @@
 test legalizer
+target aarch64
 target i686
 
 function %foo() -> i64 {

cranelift/filetests/filetests/legalizer/isplit-bb.clif

@@ -1,4 +1,5 @@
 test legalizer
+target aarch64
 target x86_64
 
 function u0:0(i128, i128, i64) -> i128 system_v {