random: Don't assume that _WIN64 implies x86_64
* random/rndw32.c: Change _WIN64 ifdef into __x86_64__.
This fixes building this file for windows on aarch64.
(cherry picked from commit ed41d6d6fb4551342b22ef763de1bd60e964e186)
- Signed-off-by: Martin Storsjö <martin@martin.st>