[x64] Add i64x2.abs

This instruction has a single instruction lowering in AVX512F/VL and a three instruction lowering in AVX but neither is currently supported in the x64 backend. To implement this, we instead subtract the vector from 0 and use a blending instruction to pick the lanes containing the absolute value.

cranelift/codegen/src/isa/x64/inst/args.rs

@@ -470,6 +470,7 @@ pub enum SseOpcode {
     Andpd,
     Andnps,
     Andnpd,
+    Blendvpd,
     Comiss,
     Comisd,
     Cmpps,
@@ -758,7 +759,8 @@ impl SseOpcode {
             | SseOpcode::Palignr
             | SseOpcode::Pshufb => SSSE3,
 
-            SseOpcode::Insertps
+            SseOpcode::Blendvpd
+            | SseOpcode::Insertps
             | SseOpcode::Packusdw
             | SseOpcode::Pcmpeqq
             | SseOpcode::Pextrb
@@ -816,6 +818,7 @@ impl fmt::Debug for SseOpcode {
             SseOpcode::Andps => "andps",
             SseOpcode::Andnps => "andnps",
             SseOpcode::Andnpd => "andnpd",
+            SseOpcode::Blendvpd => "blendvpd",
             SseOpcode::Cmpps => "cmpps",
             SseOpcode::Cmppd => "cmppd",
             SseOpcode::Cmpss => "cmpss",