asmlinkage Make __stack_chk_failed and memcmp visible

In LTO symbols implicitely referenced by the compiler need
to be visible. Earlier these symbols were visible implicitely
from being exported, but we disabled implicit visibility fo
 EXPORTs when modules are disabled to improve code size. So
now these symbols have to be marked visible explicitely.

Do this for __stack_chk_fail (with stack protector)
and memcmp.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1391845930-28580-10-git-send-email-ak@linux.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

kernel/panic.c

@@ -459,7 +459,7 @@ EXPORT_SYMBOL(warn_slowpath_null);
  * Called when gcc's -fstack-protector feature is used, and
  * gcc detects corruption of the on-stack canary value
  */
-void __stack_chk_fail(void)
+__visible void __stack_chk_fail(void)
 {
 	panic("stack-protector: Kernel stack is corrupted in: %p\n",
 		__builtin_return_address(0));

lib/string.c

@@ -648,7 +648,7 @@ EXPORT_SYMBOL(memmove);
  * @count: The size of the area.
  */
 #undef memcmp
-int memcmp(const void *cs, const void *ct, size_t count)
+__visible int memcmp(const void *cs, const void *ct, size_t count)
 {
 	const unsigned char *su1, *su2;
 	int res = 0;