Skip test_arch_m68k_detail and test_arch_tms320c64x_detail on big endian
systems.

 * Failures reported upstream test_arch_tms320c64x_detail
 * Not a regression compared to the situation in testing at the time of
   writing the patch.
 * Failures were causing problems for testing migration of libc crate
   due to the fact that the tests were skipped in plain testing tests
   but run for unstable -> testing migration tests.

--- a/src/test.rs
+++ b/src/test.rs
@@ -1799,6 +1799,7 @@
     );
 }
 
+#[cfg(target_endian = "little")]
 #[test]
 fn test_arch_m68k_detail() {
     use crate::arch::m68k::M68kOperand::*;
@@ -2559,6 +2560,7 @@
     );
 }
 
+#[cfg(target_endian = "little")]
 #[test]
 fn test_arch_tms320c64x_detail() {
     use crate::arch::tms320c64x::{