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)
(cherry picked from commit 8ed990f5)