8643 Fix misuse of _KMEMUSER in i86pc
There was some discussion of this on the developers list.  See the subject:

Request 417: 8007 uts: sysmacros.h should allow offsetof for early boot
Basically, some time (long ago) someone apparently hacked their way around

some kind of symbol exposure problem by adding -D_KMEMUSER in places that

really are not what that define was meant for, which is:

User-level code that needs to compile with some structures (etc.)

that would otherwise only be exposed when building kernel components.
Kernel components normally build with -D_KERNEL so in headers,

when defining structures etc, those are often inside an:
 #if defined(_KERNEL) || defined(_KMEMUSRER)

On the other hand, function prototypes etc. normall are in just:
 #if defined(_KERNEL)


Also relevant to this is "stand-alone" boot programs, which also

use many of the system heders with -D_BOOT which works similarly

to -D_KERNEL but may expose a different subset of things.
For that reason, many system headers have #if conditionals like:
 #if defined(_KERNEL) || defined(_KMEMUSRER) || defined(_BOOT)


Anyway, that's the normal purpose of all those defines.

As you can see in the diff shown here, the -D_KMEMUSER

define was mis-used in somewhat odd ways.

I compared the workspace (using wsdiff) before and after this change.

There were no differences other than the expected few things like

dtrace object sections, and executables that compile-in dates.