Adding arch based cfgs to crc64 checksum for x86

The crc64fast-nvme crate uses some 64 bit intrinsics that do not exist
on 32 bit x86

rust-runtime/aws-smithy-checksums/src/lib.rs

@@ -359,11 +359,9 @@ mod tests {
         Crc32, Crc32c, Md5, Sha1, Sha256,
     };
 
+    use crate::http::HttpChecksum;
     use crate::ChecksumAlgorithm;
-    use crate::{
-        http::{HttpChecksum, CRC_64_NVME_HEADER_NAME},
-        Crc64Nvme,
-    };
+
     use aws_smithy_types::base64;
     use http::HeaderValue;
     use pretty_assertions::assert_eq;
@@ -415,6 +413,7 @@ mod tests {
     #[test]
     #[cfg(not(target_arch = "x86"))]
     fn test_crc64nvme_checksum() {
+        use crate::{http::CRC_64_NVME_HEADER_NAME, Crc64Nvme};
         let mut checksum = Crc64Nvme::default();
         checksum.update(TEST_DATA.as_bytes());
         let checksum_result = Box::new(checksum).headers();