malloc: do not redzone-wrap a MemGuard allocation

[nick_spun.io]

Summary

redzone(9) documents that it skips MemGuard allocations, and the free and
realloc paths rely on a MemGuard pointer never being redzone-wrapped. With
DEBUG_MEMGUARD and DEBUG_REDZONE both set, the UMA zone-sampling path broke
this: redzone_setup() shifted the pointer into MemGuard's metadata, so the
later memguard_free() or memguard_realloc() panicked.

Skip redzone setup for a MemGuard address, matching the by-type path and
the documented behavior.

[nick_spun.io]

fix missing includes

[adrian]

oh holy crap how'd you trip over this?

[nick_spun.io]

In D60608#1390028, @adrian wrote:

oh holy crap how'd you trip over this?

I am running sys/amd64/conf/NICK-DEV-EXTRABIGASSDEBUG

I have basically everything enabled on my workstation except of KASAN (since it doesn't play nicely with others and the performance hit is insane)