Fix build error on big endian aarch64

Author: taiki-e

crates/core_simd/src/vendor/arm.rs

@@ -69,7 +69,7 @@ mod simd32 {
     from_transmute! { unsafe Simd<i8, 4> => int8x4_t }
 }
 
-#[cfg(target_arch = "aarch64")]
+#[cfg(all(target_arch = "aarch64", target_endian = "little"))]
 mod aarch64 {
     use super::neon::*;
     use super::*;