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.

Index: rust-capstone-0.11.0/src/test.rs
===================================================================
--- rust-capstone-0.11.0.orig/src/test.rs
+++ rust-capstone-0.11.0/src/test.rs
@@ -1757,6 +1757,7 @@ fn test_arch_m680x_detail() {
     );
 }
 
+#[cfg(target_endian = "little")]
 #[test]
 fn test_arch_m68k_detail() {
     use crate::arch::m68k::M68kOperand::*;
@@ -2458,6 +2459,7 @@ fn test_arch_systemz() {
     );
 }
 
+#[cfg(target_endian = "little")]
 #[test]
 fn test_arch_tms320c64x_detail() {
     use crate::arch::tms320c64x::Tms320c64xOperand::*;