Check for the extended mnemonic

It is what objdump produces usually.

Author: lu-zero

coresimd/powerpc64/vsx.rs

@@ -231,9 +231,11 @@ mod sealed {
         unsafe fn vec_xxpermdi(self, b: Self, dm: u8) -> Self;
     }
 
+    // xxpermdi has an big-endian bias and extended mnemonics
     #[inline]
     #[target_feature(enable = "vsx")]
-    #[cfg_attr(test, assert_instr(xxpermdi, dm = 0x0))]
+    #[cfg_attr(and(test, target_endian="little"), assert_instr(xxmrgld, dm = 0x0))]
+    #[cfg_attr(and(test, target_endian="big"), assert_instr(xxspltd, dm = 0x0))]
     unsafe fn xxpermdi(a: i64x2, b: i64x2, dm: u8) -> i64x2 {
         match dm & 0b11 {
             0 => simd_shuffle2(a, b, [0b00, 0b10]),