[Bug sanitizer/85230] asan: false positives in kernel on allocas

[dvyukov at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85230

--- Comment #2 from Dmitry Vyukov <dvyukov at google dot com> ---
The runtime callbacks look correct to me, and the shadow they produce also
looks reasonable: 32-byte rezone before, 32 + (32 - object size) redzone after:

 ffff8800247b7180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8800247b7200: 00 00 00 00 ca ca ca ca 02 cb cb cb cb cb cb cb
                                     ^
 ffff8800247b7280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00