nx_x86_basic_test.nx

nx_x86_basic_test.nx -- minimal syscall-free smoke for x86_64. Tests basic i64 arithmetic + control flow + the codegen patterns our AI primitives rely on (loops, bitwise ops, comparisons). No sys_mmap, no sys_write, no syscalls -- so it runs identically on any target the x86_64 / RV64 / etc. backend supports. PASS criterion: main() returns 0. Any non-zero return = assertion failure encoded in the return code.