compiler: expression version of QEMU_BUILD_BUG_ON

compiler: expression version of QEMU_BUILD_BUG_ON

QEMU_BUILD_BUG_ON uses a typedef in order to be safe
to use outside functions, but sometimes it's useful
to have a version that can be used within an expression.
Following what Linux does, introduce QEMU_BUILD_BUG_ON_ZERO
that return zero after checking condition at build time.

Signed-off-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>