Linux 5.0 compat: ASM_BUG macro

The 5.0 kernel defines the macro ASM_BUG. In order to prevent a
conflict and build failure rename ASM_BUG to ZFS_ASM_BUG. This
is currently only an issue on aarch64 but all instances of
ASM_BUG we're renamed to avoid any future conflict on x86_64.

Reviewed-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Reviewed-by: Chris Dunlop <chris@onthe.net.au>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8725
Issue #8545