NMAKE: inconclusive tests with inheriting cmdline macros... WTF?

[xparq]

• On the one hand, I had the initial experience, when I first learned about the problem at all... It seemed to not have (working) support for that actually (hence the cringy workaround).
  • This assumption was later reinforced by learning that NMAKE 1.20 used to have /V for inheriting macros, but (my current) v14 doesn't have that option any more. (But that proved to be a red herring: it meant inheriting all macros, in addition to those defined on the cmdline! (Still very interesting why they abandoned that feature. I guess it may have introduced issues regarding what should override what; also.)
• OTOH, I can't reproduce it now (-> e.g. x1ab: NMAKE studies...).
• But even there, I did have a failure case, when it had broken the propagation of that macro (when I tried to also add a loop guard macro to the child cmdline)...
• But, but... then again, after getting rid of that (by not looping), and adding another macro on the cmdline later...: just can't seem to get the same error yet again... :-o

[xparq]

Move this to x1ab and only ref. it here.