games/eureka: fix build on powerpc64 head

clang can't build this code:
In file included from src/e_basis.cc:27:
In file included from src/main.h:86:
src/sys_endian.h:66:58: error: unsupported inline asm: input with type 'int' matching output with type 'u16_t' (aka 'unsigned short')

__asm__("rlwimi %0,%2,8,16,23" : "=&r" (result) : "0" (x >> 8), "r" (x));

Approved by: tier 2 blanket