reg_id_t width check broken by OPSZ_NA=0
I noticed that 053f6b6a PR #3497 broke this check:
* The reg_id_t type is now wider, but for x86 we ensure our values
* all fit via an assert in d_r_arch_init().
That PR set OPSZ_NA to 0, which broke the check, which I believe is this:
IF_X86(ASSERT(CHECK_TRUNCATE_TYPE_byte(OPSZ_LAST)));