rts: use XXH3_64bits hash on all 64-bit platforms

This commit enables XXH3_64bits hash to be used on all 64-bit
platforms. Previously it was only enabled on x86_64, so platforms like
aarch64 silently falls back to using XXH32 which degrades the hashing
function quality.

(cherry picked from commit 4a97bdb8)

rts/Hash.c

@@ -99,7 +99,7 @@ int
 hashStr(const HashTable *table, StgWord w)
 {
     const char *key = (char*) w;
-#if defined(x86_64_HOST_ARCH)
+#if WORD_SIZE_IN_BITS == 64
     StgWord h = XXH3_64bits_withSeed (key, strlen(key), 1048583);
 #else
     StgWord h = XXH32 (key, strlen(key), 1048583);