kernel build environment versioning?

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

Is there any kind of preprocessor-testable version ID when building the
kernel?  If so, how far back does it go?  I had a quick look at the
three versions I care about (using -dM -E) and none of them seemed to
define any sort of version symbol, but perhaps I'd just need to add an
include file my test missed or something.

The reason I care is that I have a kernel facility (diskwatch, the
kernel part of my live-backup code) for which I'd like to share code
across versions to the extent possible.  This would be greatly
facilitated by something that would let me do it as

#if ...on version X...
...setup for version X...
#elif ...on version Y...
...setup for version Y...
#elif ...on version Z...
...setup for version Z...
#else
...error out...
#endif
...bulk of the code, using the stuff set up above...

But this works only when the preprocessor can tell whether the file is
being built for a 1.4T kernel versus 3.1 versus 4.0.1 versus 5.0 versus
whatever.  I don't really expect anyone to remember what 1.4T has, but
for 5.x and 4.x and maybe even 3.x I figure if there is anything of the
sort, someone here will know it.

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