c/r: prctl: fix build error for no-MMU case

Commit 1ad75b9 ("c/r: prctl: add minimal address test to
PR_SET_MM") added some address checking to prctl_set_mm() used by
checkpoint-restore.  This causes a build error for no-MMU systems:

   kernel/sys.c: In function 'prctl_set_mm':
   kernel/sys.c:1868:34: error: 'mmap_min_addr' undeclared (first use in this function)

The test for mmap_min_addr doesn't make a lot of sense for no-MMU code
as noted in commit 6e14154 ("NOMMU: Optimise away the
{dac_,}mmap_min_addr tests").

This patch defines mmap_min_addr as 0UL in the no-MMU case so that the
compiler will optimize away tests for "addr < mmap_min_addr".

Signed-off-by: Mark Salter <[email protected]>
Reviewed-by: Cyrill Gorcunov <[email protected]>
Cc: <[email protected]>	[3.6.x]
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

include/linux/security.h

@@ -118,6 +118,7 @@ void reset_security_ops(void);
 extern unsigned long mmap_min_addr;
 extern unsigned long dac_mmap_min_addr;
 #else
+#define mmap_min_addr		0UL
 #define dac_mmap_min_addr	0UL
 #endif