ignore 32-bit for dont-shuffle-bswaps

Author: workingjubilee

tests/codegen/dont-shuffle-bswaps.rs

@@ -1,6 +1,8 @@
 //@ revisions: OPT2 OPT3
 //@[OPT2] compile-flags: -Copt-level=2
 //@[OPT3] compile-flags: -C opt-level=3
+// some targets don't do the opt we are looking for
+//@[OPT3] only-64bit
 //@ min-llvm-version: 18.1.3
 
 #![crate_type = "lib"]