[S390] uaccess: implement strict user copy checks

Same as on x86 and sparc, besides the fact that enabling the option
will just emit compile time warnings instead of errors.
Keeps allyesconfig kernels compiling.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig.debug

@@ -6,4 +6,17 @@ config TRACE_IRQFLAGS_SUPPORT
 
 source "lib/Kconfig.debug"
 
+config DEBUG_STRICT_USER_COPY_CHECKS
+	bool "Strict user copy size checks"
+	---help---
+	  Enabling this option turns a certain set of sanity checks for user
+	  copy operations into compile time warnings.
+
+	  The copy_from_user() etc checks are there to help test if there
+	  are sufficient security checks on the length argument of
+	  the copy operation, by having gcc prove that the argument is
+	  within bounds.
+
+	  If unsure, or if you run an older (pre 4.4) gcc, say N.
+
 endmenu