Run endianess-dependent tests under #[cfg(target_endian = "little")] (#452, #451)

Author: tyranron

tests/debug.rs

@@ -784,6 +784,7 @@ mod structs {
             }
         }
 
+        #[cfg(target_endian = "little")]
         mod r#unsized {
             #[cfg(not(feature = "std"))]
             use alloc::format;

tests/display.rs

@@ -786,6 +786,7 @@ mod structs {
             }
         }
 
+        #[cfg(target_endian = "little")]
         mod r#unsized {
             use super::*;