Fix ABI mismatch in packed HIO request

Using size_t etc. is incorrect, since these definitions are based on the
build machine which most likely has a different arch than the 3DS.

src/core/gdbstub/hio.h

@@ -17,11 +17,11 @@ struct PackedGdbHioRequest {
     char param_format[8 + 1];
 
     u64 parameters[8];
-    size_t string_lengths[8];
+    u32 string_lengths[8];
 
     // Return
     s64 retval;
-    int gdb_errno;
+    s32 gdb_errno;
     bool ctrl_c;
 };