Kconfig: consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

Kconfig: consolidate CONFIG_DEBUG_STRICT_USER_COPY_CHECKS

The help text for this config is duplicated across the x86, parisc, and
s390 Kconfig.debug files.  Arnd Bergman noted that the help text was
slightly misleading and should be fixed to state that enabling this
option isn't a problem when using pre 4.4 gcc.

To simplify the rewording, consolidate the text into lib/Kconfig.debug
and modify it there to be more explicit about when you should say N to
this config.

Also, make the text a bit more generic by stating that this option
enables compile time checks so we can cover architectures which emit
warnings vs.  ones which emit errors.  The details of how an
architecture decided to implement the checks isn't as important as the
concept of compile time checking of copy_from_user() calls.

While we're doing this, remove all the copy_from_user_overflow() code
that's duplicated many times and place it into lib/ so that any
architecture supporting this option can get the function for free.

Signed-off-by: Stephen Boyd <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Acked-by: H. Peter Anvin <[email protected]>
Cc: Arjan van de Ven <[email protected]>
Acked-by: Helge Deller <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Chris Metcalf <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>