LinuxKPI: change BUILD_BUG_ON()

[bz]

Summary

BUILD_BUG_ON() can be used inside functions where the definition to
CTASSERT() (_Static_assert()) seems to not work.
Go back to an old-style CTASSERT() implementation but also add a
variable dclaration to avoid "unsued typedef" errors and dummy-use
the variable to avoid "unusued variable" errors. Given it is all
self-contained in a block and not used outside this should be
optimised away.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Reviewed by:
Differential Revision:

[• hselasky]

sys/compat/linuxkpi/common/include/linux/kernel.h

101

Should this be enclosed with while (0) and not "do { } while (0) "?

[bz]

sys/compat/linuxkpi/common/include/linux/kernel.h

101

Would a while (0) { } be optimized out without ever entering the block because it can never happen?

[• hselasky]

sys/compat/linuxkpi/common/include/linux/kernel.h

101

Yes, with -O2, but after parsing the code. So I believe any asserts will trigger.

[bz]

Switch to while (0) { } as suggested by @hselasky