This generates noticeably better code since we don't need to test the
error register etc, the exception just jumps to the error handling
directly.

Unlike get_user(), there's no need to worry about old compilers. All
supported compilers support the regular non-output 'asm goto', as
pointed out by Nathan Chancellor.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>