MMIO:read64 formats values above LUA_MAXINTEGER with "0x%lux": %lu
prints decimal and the trailing x is literal, so 2^63 comes back as
"0x9223372036854775808x". On 32-bit targets %lu is also the wrong
width for a uint64_t. Print it as hex with PRIx64.

--- a/src/lua_mmio.c
+++ b/src/lua_mmio.c
@@ -11,6 +11,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdint.h>
+#include <inttypes.h>
 #include <errno.h>
 
 #include <mmio.h>
@@ -169,7 +170,7 @@
 
     if (value > LUA_MAXINTEGER) {
         char buf[24];
-        snprintf(buf, sizeof(buf), "0x%lux", value);
+        snprintf(buf, sizeof(buf), "0x%" PRIx64, value);
         lua_pushstring(L, buf);
     } else {
         lua_pushlargeinteger(L, value);